/* ============================================================
   HỌC HÓA THÔNG MINH — Main Stylesheet
   Phong cách neo-brutalism + paper (theo thiết kế mẫu)
   ============================================================ */
:root{
  --paper:#FBF7EF;
  --paper-2:#F4EEE0;
  --paper-tint:#FFF3DC;
  --ink:#15171B;
  --ink-soft:#59524A;
  --ink-faint:#8B8377;
  --muted:#6B6B76;
  --line:#E7E0CF;
  --line-strong:rgba(22,19,17,0.4);
  --flame:#FF5A36;
  --cobalt:#2C5FCF;
  --copper:#0FA57B;
  --gold:#F5A800;
  --white:#FFFFFF;
  --electron:#6C4CF1;
  --electron-tint:#E9E3FF;
  --chloro:#1F9D53;
  --chloro-tint:#DCF3E3;
  --citrine:#F5B400;
  --citrine-tint:#FFF0C2;
  --litmus:#FF3E86;
  --litmus-tint:#FFE1EC;
  --sky:#2170C7;
  --sky-tint:#DDEBFB;
  --lab-night:#1B1730;
  --lab-night-2:#26213F;
  --danger:#E5484D;
  --radius-lg:22px;
  --radius-md:16px;
  --radius:14px;
  --radius-sm:10px;
  --shadow-hard:5px 5px 0 var(--ink);
  --shadow-soft:0 1px 2px rgba(22,19,17,0.06);
}

*{ margin:0; padding:0; box-sizing:border-box; }
html{ scroll-behavior:smooth; }

body{
  background:var(--paper);
  color:var(--ink);
  font-family:'Inter',sans-serif;
  -webkit-font-smoothing:antialiased;
  overflow-x:hidden;
  min-height:100vh;
  display:flex;
  flex-direction:column;
}

/* ---------- Background decoration ---------- */
.bg-decor{
  position:fixed; inset:0; z-index:0; pointer-events:none; overflow:hidden; contain:strict;
}
.bg-decor::before{
  content:""; position:absolute; inset:0; will-change:auto;
  background-image:radial-gradient(circle, rgba(21,23,27,0.07) 1px, transparent 1px);
  background-size:26px 26px;
  mask-image:radial-gradient(ellipse 70% 60% at 50% 30%, black 40%, transparent 90%);
  -webkit-mask-image:radial-gradient(ellipse 70% 60% at 50% 30%, black 40%, transparent 90%);
}
.blob{ position:absolute; border-radius:50%; filter:blur(40px); opacity:.35; contain:layout size; }
.blob-1{ width:480px; height:480px; top:-160px; left:-120px; background:var(--cobalt); opacity:.18; }
.blob-2{ width:420px; height:420px; top:120px; right:-160px; background:var(--flame); opacity:.16; }
.blob-3{ width:380px; height:380px; bottom:-140px; left:38%; background:var(--copper); opacity:.14; }
.orbit-ring{
  position:absolute; top:50%; left:50%;
  border:1.5px solid rgba(21,23,27,.1); border-radius:50%;
  transform:translate(-50%,-50%);
}
.orbit-ring.r1{ width:640px; height:640px; animation:spin 80s linear infinite; will-change:transform; }
.orbit-ring.r2{ width:480px; height:480px; animation:spin 60s linear infinite reverse; will-change:transform; }
.orbit-ring.r3{ width:820px; height:820px; animation:spin 110s linear infinite; will-change:transform; }
.orbit-ring span{
  position:absolute; width:9px; height:9px; border-radius:50%;
  top:-5px; left:50%; box-shadow:0 0 10px currentColor;
}
.orbit-ring.r1 span{ background:var(--flame); color:var(--flame); }
.orbit-ring.r2 span{ background:var(--cobalt); color:var(--cobalt); }
.orbit-ring.r3 span{ background:var(--copper); color:var(--copper); }
@keyframes spin{ to{ transform:translate(-50%,-50%) rotate(360deg); } }
@media (prefers-reduced-motion: reduce){ .orbit-ring{ animation:none !important; } *{ animation-duration:.001ms !important; } }

/* ---------- Header ---------- */
header.site{ position:relative; z-index:20; border-bottom:1.5px solid var(--line); background:rgba(251,247,239,.85); backdrop-filter:blur(8px); }
.header-inner{ display:flex; align-items:center; justify-content:space-between; gap:18px; padding:16px 0; flex-wrap:wrap; }
.brand{ display:flex; align-items:center; gap:12px; text-decoration:none; color:inherit; }
.logo-mark{
  width:42px; height:42px; border-radius:12px; display:flex; align-items:center; justify-content:center;
  background:var(--ink); overflow:hidden; flex-shrink:0;
}
.logo-mark img{ width:100%; height:100%; object-fit:cover; display:block; }
.logo-fallback{
  background:
    radial-gradient(circle at 35% 40%, var(--cobalt) 0 6px, transparent 6.5px),
    radial-gradient(circle at 65% 35%, var(--flame) 0 4px, transparent 4.5px),
    radial-gradient(circle at 58% 65%, var(--copper) 0 5px, transparent 5.5px),
    radial-gradient(circle at 50% 50%, var(--white) 0 3px, transparent 3.5px);
}
.brand-name{
  font-family:'Space Grotesk',sans-serif; font-weight:700; font-size:16.5px; letter-spacing:.2px; color:var(--ink);
}
.brand-name small{
  display:block; font-family:'IBM Plex Mono',monospace; font-weight:500; font-size:10.5px;
  letter-spacing:.8px; color:var(--muted); text-transform:uppercase; margin-top:2px;
}

.main-nav{ display:flex; gap:4px; flex-wrap:wrap; }
.nav-link{
  font-family:'Space Grotesk',sans-serif; font-weight:600; font-size:13.5px;
  color:var(--muted); text-decoration:none; padding:9px 16px; border-radius:10px;
  transition:color .18s ease, background .18s ease;
}
.nav-link:hover, .nav-link.active{ color:var(--ink); background:var(--paper-2); }

.header-cta{ display:flex; gap:10px; align-items:center; }
.link-btn{
  font-family:'Space Grotesk',sans-serif; font-weight:600; font-size:13.5px; color:var(--ink);
  text-decoration:none; padding:9px 18px; border-radius:10px; border:1.5px solid transparent;
  transition:border-color .18s ease, background .18s ease;
}
.link-btn.ghost:hover{ border-color:var(--line); background:var(--white); }
.link-btn.solid{ background:var(--ink); color:var(--white); border-color:var(--ink); }
.link-btn.solid:hover{ background:#2a2d33; }
.link-btn.danger{ color:var(--danger); }

/* Avatar dropdown */
.avatar-wrap{ position:relative; }
.avatar{
  width:38px; height:38px; border-radius:10px; color:#fff; font-weight:700; font-size:14px;
  display:flex; align-items:center; justify-content:center; cursor:pointer;
  box-shadow:var(--shadow-soft);
}
.avatar-drop{
  position:absolute; right:0; top:calc(100% + 10px); min-width:200px; background:var(--card, #fff);
  border:1.5px solid var(--line); border-radius:var(--radius); box-shadow:0 10px 28px rgba(22,19,17,0.12);
  padding:8px; display:none; z-index:30;
}
.avatar-wrap:hover .avatar-drop, .avatar-wrap.open .avatar-drop{ display:block; }
.avatar-drop a{ display:block; padding:9px 11px; border-radius:8px; font-weight:500; font-size:14px; color:var(--ink-soft); text-decoration:none; }
.avatar-drop a:hover{ background:var(--paper-tint); color:var(--ink); }
.avatar-drop a.danger{ color:var(--danger); }

.menu-toggle{ display:none; background:var(--white); border:1.5px solid var(--line); border-radius:10px; padding:8px 12px; font-size:18px; cursor:pointer; }

/* ---------- Main & Footer ---------- */
.main-content{ position:relative; z-index:1; flex:1; padding:36px 28px 60px; }
.wrap{ max-width:1120px; margin:0 auto; padding:0 28px; }

footer.site{ position:relative; z-index:1; border-top:1.5px solid var(--line); margin-top:40px; background:rgba(251,247,239,.7); }
footer.site .wrap{ padding-top:44px; padding-bottom:32px; }
.footer-grid{ display:grid; grid-template-columns:1.4fr 1fr 1fr; gap:36px; margin-bottom:28px; }
.footer-grid ul{ list-style:none; margin-top:10px; }
.footer-grid li{ margin-bottom:7px; }
.footer-grid a{ color:var(--muted); font-size:13.5px; text-decoration:none; }
.footer-grid a:hover{ color:var(--ink); }
.footer-bottom{ text-align:center; font-family:'IBM Plex Mono',monospace; font-size:12px; color:var(--muted); padding-top:20px; border-top:1px solid var(--line); }

/* ---------- Alert / Flash ---------- */
.alert{ padding:13px 18px; border-radius:var(--radius-sm); margin-bottom:18px; font-size:14px; font-weight:600; border:1.5px solid var(--line); background:var(--white); box-shadow:var(--shadow-soft); }
.alert-success{ border-left:5px solid var(--chloro); background:var(--chloro-tint); }
.alert-error{ border-left:5px solid var(--danger); background:#FDE8E8; }
.alert-info{ border-left:5px solid var(--cobalt); background:var(--sky-tint); }

/* ---------- Buttons ---------- */
.btn{
  font-family:'Space Grotesk',sans-serif; font-weight:700; font-size:14.5px; text-decoration:none;
  padding:12px 24px; border-radius:12px; border:2px solid var(--ink); display:inline-block;
  cursor:pointer; transition:transform .12s ease, box-shadow .12s ease; background:transparent; color:var(--ink);
}
.btn-primary{ background:var(--gold); color:var(--ink); box-shadow:4px 4px 0 var(--ink); }
.btn-secondary{ background:var(--white); color:var(--ink); box-shadow:4px 4px 0 var(--ink); }
.btn-dark{ background:var(--ink); color:var(--white); border-color:var(--ink); }
.btn-electron{ background:var(--electron); color:#fff; border-color:var(--electron); }
.btn-chloro{ background:var(--chloro); color:#fff; border-color:var(--chloro); }
.btn-ghost{ box-shadow:none; border-color:var(--line); }
.btn:hover{ transform:translate(-2px,-2px); box-shadow:6px 6px 0 var(--ink); }
.btn-primary:hover, .btn-secondary:hover{ box-shadow:6px 6px 0 var(--ink); }
.btn:active{ transform:translate(1px,1px); box-shadow:2px 2px 0 var(--ink); }
.btn:disabled{ opacity:.5; cursor:not-allowed; transform:none; }
.btn-sm{ padding:8px 16px; font-size:13px; }

/* ---------- Cards ---------- */
.card{
  background:var(--white); border:1.5px solid var(--line); border-radius:var(--radius-lg);
  padding:24px; box-shadow:var(--shadow-soft);
}
.card.signature{ border:2px solid var(--ink); box-shadow:var(--shadow-hard); }
.card h3{ font-family:'Space Grotesk',sans-serif; font-size:17px; margin-bottom:8px; }

/* ---------- Splash / Landing ---------- */
.splash{ padding:90px 0 70px; text-align:center; display:flex; flex-direction:column; align-items:center; }
.eyebrow{
  display:inline-flex; align-items:center; gap:8px; font-family:'IBM Plex Mono',monospace;
  font-size:11.5px; font-weight:600; letter-spacing:1.4px; text-transform:uppercase;
  color:var(--copper); background:rgba(15,165,123,.09); border:1px solid rgba(15,165,123,.25);
  padding:7px 14px; border-radius:999px; margin-bottom:26px; text-decoration:none;
}
.eyebrow::before{ content:"⚛"; font-size:13px; }
.splash h1{
  font-family:'Space Grotesk',sans-serif; font-weight:700; font-size:clamp(2rem, 5vw, 3.2rem);
  line-height:1.15; letter-spacing:-.5px; max-width:680px;
}
.splash p{ font-size:16px; color:var(--muted); max-width:480px; margin-top:18px; line-height:1.6; }
.splash-cta{ display:flex; gap:14px; margin-top:36px; flex-wrap:wrap; justify-content:center; }

/* Features */
.feature-grid{ display:grid; grid-template-columns:repeat(4,1fr); gap:16px; margin-top:24px; }
.feature-card{ padding:22px 18px; cursor:pointer; text-decoration:none; color:inherit; display:block; transition:transform .12s, box-shadow .12s; }
.feature-card:hover{ transform:translateY(-3px); box-shadow:0 10px 24px rgba(22,19,17,0.1); }
.feature-icon{ width:44px; height:44px; border-radius:11px; display:flex; align-items:center; justify-content:center; font-size:21px; margin-bottom:14px; }
.feature-card h3{ font-size:15px; margin-bottom:6px; }
.feature-card p{ font-size:13px; color:var(--ink-soft); line-height:1.5; }

.section-head{ text-align:center; margin:56px 0 28px; }
.section-head h2{ font-family:'Space Grotesk',sans-serif; font-size:clamp(1.5rem,3vw,2rem); font-weight:700; }
.section-head p{ color:var(--muted); font-size:14.5px; margin-top:8px; }

/* Stats hero */
.hero-stats{ display:flex; gap:34px; margin-top:40px; flex-wrap:wrap; justify-content:center; }
.stat{ text-align:center; }
.stat b{ display:block; font-family:'Space Grotesk',sans-serif; font-size:22px; font-weight:700; }
.stat span{ font-family:'IBM Plex Mono',monospace; font-size:10.5px; color:var(--muted); text-transform:uppercase; letter-spacing:.6px; }

/* ---------- Level select ---------- */
.levels-section{ padding:32px 0 20px; }
.level-grid{ display:grid; grid-template-columns:repeat(3, 1fr); gap:22px; }
.level-card{
  position:relative; background:var(--white); border:2px solid var(--ink); border-radius:var(--radius-lg);
  padding:26px 24px; text-align:left; cursor:pointer; font-family:inherit; color:inherit;
  transition:transform .15s ease; outline:none;
}
.level-card:hover{ transform:translate(-3px,-3px); box-shadow:var(--shadow-hard); }
.level-card.selected{ background:var(--citrine-tint); border-color:var(--citrine); }
.level-top{ display:flex; align-items:center; justify-content:space-between; margin-bottom:18px; }
.level-num{ font-family:'IBM Plex Mono',monospace; font-size:13px; color:var(--muted); }
.level-badge{
  width:44px; height:44px; border-radius:12px; background:var(--ink); color:var(--white);
  display:flex; align-items:center; justify-content:center; font-family:'Space Grotesk',sans-serif;
  font-weight:700; font-size:16px;
}
.level-card h3{ font-family:'Space Grotesk',sans-serif; font-size:20px; margin-bottom:8px; }
.level-card p{ font-size:14px; color:var(--muted); line-height:1.6; margin-bottom:18px; min-height:66px; }
.level-meta{ display:flex; align-items:center; justify-content:space-between; }
.difficulty{ display:flex; gap:5px; }
.difficulty i{ width:26px; height:8px; border-radius:999px; background:var(--paper-2); display:block; }
.difficulty i.on{ background:var(--flame); }
.level-arrow{ font-family:'Space Grotesk',sans-serif; font-weight:700; font-size:14px; color:var(--copper); }
.confirm-panel{
  margin-top:34px; background:var(--white); border:2px solid var(--ink); border-radius:var(--radius-lg);
  padding:34px; text-align:center; box-shadow:var(--shadow-hard); display:none;
}
.confirm-panel.visible{ display:block; animation:popIn .35s ease; }
@keyframes popIn{ from{ opacity:0; transform:scale(.94); } to{ opacity:1; transform:scale(1); } }
.chip{
  display:inline-block; font-family:'IBM Plex Mono',monospace; font-size:12px; background:var(--paper-2);
  border:1.5px solid var(--line); border-radius:999px; padding:6px 16px; margin-bottom:14px;
}
.confirm-panel h3{ font-family:'Space Grotesk',sans-serif; font-size:22px; margin-bottom:10px; }
.confirm-panel p{ color:var(--muted); margin-bottom:22px; }
.confirm-actions{ display:flex; gap:14px; justify-content:center; flex-wrap:wrap; }

/* ---------- Auth pages ---------- */
.auth-wrap{ max-width:440px; margin:44px auto 0; }
.auth-card{ background:var(--white); border:2px solid var(--ink); border-radius:var(--radius-lg); padding:36px 32px; box-shadow:var(--shadow-hard); }
.auth-card h2{ font-family:'Space Grotesk',sans-serif; font-size:24px; margin-bottom:6px; }
.auth-card .sub{ color:var(--muted); font-size:14px; margin-bottom:26px; }
.form-group{ margin-bottom:18px; }
.form-group label{ display:block; font-family:'Space Grotesk',sans-serif; font-weight:600; font-size:13.5px; margin-bottom:7px; }
.form-control{
  width:100%; padding:12px 14px; border:1.5px solid var(--ink); border-radius:var(--radius-sm);
  font-size:14.5px; font-family:inherit; background:var(--paper); transition:border-color .15s;
}
.form-control:focus{ outline:none; border-color:var(--cobalt); background:var(--white); }
textarea.form-control{ min-height:120px; resize:vertical; }
.form-hint{ font-size:12px; color:var(--muted); margin-top:6px; }
.form-footer{ text-align:center; margin-top:22px; font-size:14px; color:var(--muted); }
.form-footer a{ color:var(--cobalt); font-weight:600; }

/* ---------- Dashboard ---------- */
.dash-head{ display:flex; align-items:center; justify-content:space-between; flex-wrap:wrap; gap:16px; margin-bottom:26px; }
.greet-card{ display:flex; align-items:center; gap:18px; flex-wrap:wrap; border-left:5px solid var(--bunsen, var(--flame)); border-radius:0 var(--radius-lg) var(--radius-lg) 0; }
.greet-avatar{ width:60px; height:60px; border-radius:var(--radius); background:var(--electron-tint); display:flex; align-items:center; justify-content:center; font-size:26px; flex-shrink:0; }
.greet-info h2{ font-family:'Space Grotesk',sans-serif; font-size:22px; margin-bottom:8px; }
.greet-meta{ display:flex; gap:10px; flex-wrap:wrap; font-size:13px; }
.badge-pill{ background:var(--paper-tint); border-radius:999px; padding:6px 13px; display:inline-flex; align-items:center; gap:6px; font-weight:700; text-decoration:none; color:inherit; }
.badge-pill.mono{ font-family:'Space Mono',monospace; }
.badge-pill:hover{ background:var(--citrine-tint); }

.dash-grid{ display:grid; grid-template-columns:repeat(3,1fr); gap:16px; }
.span-3{ grid-column:1 / -1; }
.span-2{ grid-column:span 2; }

.continue-card{ background:var(--electron); color:#fff; border:none; }
.continue-card .eyebrow{ color:rgba(255,255,255,0.7); }
.continue-card h3{ font-size:18px; margin:8px 0 16px; line-height:1.4; }
.progress-track{ height:10px; background:rgba(255,255,255,0.22); border-radius:999px; overflow:hidden; margin-bottom:16px; }
.progress-fill{ height:100%; background:#fff; transition:width .4s ease; }

.journey-stats{ display:flex; gap:10px; margin:16px 0; }
.stat-box{ flex:1; background:var(--paper-tint); border-radius:var(--radius-sm); padding:12px; text-align:center; }
.stat-box .num{ font-family:'Space Mono'; font-size:20px; font-weight:700; }
.stat-box .lbl{ font-size:10.5px; color:var(--ink-soft); font-weight:700; }
.journey-note{ font-size:13px; color:var(--ink-soft); margin:12px 0 8px; line-height:1.5; }

.ai-card{ background:var(--paper-tint); }
.ai-head{ display:flex; align-items:center; gap:10px; margin-bottom:14px; }
.ai-head .icn{ width:34px; height:34px; background:var(--white); border-radius:var(--radius-sm); display:flex; align-items:center; justify-content:center; font-size:16px; }
.ai-actions{ display:flex; flex-direction:column; gap:8px; }
.ai-actions .btn{ width:100%; text-align:left; background:var(--white); font-size:13px; padding:10px 14px; }

.quick-grid{ display:grid; grid-template-columns:repeat(4,1fr); gap:10px; margin-top:6px; }
.quick-item{
  background:var(--paper-tint); border-radius:var(--radius-sm); padding:16px 8px; text-align:center;
  font-weight:700; font-size:12px; cursor:pointer; color:var(--ink-soft); text-decoration:none; display:block;
}
.quick-item:hover{ background:var(--electron-tint); color:var(--ink); }
.quick-item .qi-icon{ font-size:20px; display:block; margin-bottom:8px; }

/* Streak */
.streak-card{ background:var(--lab-night); color:#fff; border-radius:var(--radius-lg); padding:26px; display:flex; flex-direction:column; height:100%; position:relative; overflow:hidden; }
.streak-card::before{ content:''; position:absolute; top:-40px; right:-40px; width:140px; height:140px; border-radius:50%; background:radial-gradient(circle, rgba(108,76,241,0.35), transparent 70%); }
.streak-top{ display:flex; align-items:center; justify-content:space-between; margin-bottom:14px; position:relative; }
.streak-day{ display:flex; align-items:center; gap:10px; font-size:18px; font-weight:700; }
.streak-day .flame{ width:30px; height:30px; flex-shrink:0; }
.streak-month{ display:flex; align-items:center; gap:10px; font-weight:700; color:#a7a0c9; font-size:13.5px; }
.streak-month button{ background:none; border:none; color:#a7a0c9; font-size:15px; cursor:pointer; }
.streak-check{ color:var(--chloro); background:rgba(31,157,83,0.16); display:inline-flex; width:fit-content; align-items:center; gap:6px; font-weight:700; font-size:12.5px; margin-bottom:16px; padding:5px 10px; border-radius:999px; position:relative; }
.cal-grid{ display:grid; grid-template-columns:repeat(7,1fr); gap:5px; text-align:center; position:relative; }
.cal-grid .dow{ font-size:11px; color:#9C96BC; font-weight:700; margin-bottom:2px; }
.cal-day{ aspect-ratio:1; display:flex; align-items:center; justify-content:center; border-radius:50%; font-size:13px; font-weight:500; color:#B7B2D4; position:relative; }
.cal-day.done{ background:rgba(31,157,83,0.85); color:#fff; font-weight:700; }
.cal-day.today{ border:2px solid var(--citrine); color:var(--citrine); font-weight:700; }
.cal-day.locked{ color:#6B6592; }
.streak-full-stats{ display:flex; gap:8px; margin-top:16px; position:relative; }
.streak-full-stats .box{ flex:1; background:var(--lab-night-2); border-radius:10px; padding:10px; text-align:center; }
.streak-full-stats .box .n{ font-family:'Space Mono'; font-weight:700; font-size:17px; }
.streak-full-stats .box .l{ font-size:10px; color:#a7a0c9; }

/* ---------- Leaderboard ---------- */
.lb-hero{ background:var(--lab-night); color:#fff; border-radius:var(--radius-lg); padding:48px 36px; text-align:center; position:relative; overflow:hidden; }
.lb-hero .medals{ font-size:36px; margin-bottom:12px; }
.lb-hero h1{ font-family:'Space Grotesk',sans-serif; font-size:28px; margin-bottom:12px; }
.lb-hero p{ color:#c8c2e8; max-width:520px; margin:0 auto; font-size:14.5px; line-height:1.6; }
.lb-podium{ display:grid; grid-template-columns:repeat(3,1fr); gap:12px; margin:28px 0; max-width:640px; margin-left:auto; margin-right:auto; }
.podium-card{ border:1.5px solid var(--line); border-radius:var(--radius); padding:16px 10px; text-align:center; background:var(--paper-tint); }
.podium-card.first{ background:var(--citrine-tint); border-color:var(--citrine); transform:translateY(-8px); }
.podium-card .rank-emoji{ font-size:24px; }
.podium-card .pname{ font-weight:700; font-size:13.5px; margin:6px 0 2px; }
.podium-card .pexp{ font-family:'Space Mono'; font-size:11px; color:var(--ink-soft); }
.lb-table{ width:100%; border-collapse:collapse; background:var(--white); border:1.5px solid var(--line); border-radius:var(--radius-lg); overflow:hidden; }
.lb-table tr{ border-bottom:1.5px solid var(--line); }
.lb-table tr:last-child{ border-bottom:none; }
.lb-table td{ padding:13px 12px; font-size:14px; font-weight:500; }
.lb-table td.rank{ font-family:'Space Mono'; font-weight:700; width:44px; color:var(--ink-faint); }
.lb-table tr.me{ background:var(--citrine-tint); }
.lb-table td.name{ font-weight:700; }
.lb-avatar-sm{ width:28px; height:28px; border-radius:8px; display:inline-flex; align-items:center; justify-content:center; font-size:12px; font-weight:700; margin-right:8px; vertical-align:middle; color:#fff; }
.lb-table{ font-size:14px; }

/* ---------- Lesson / Quiz listing ---------- */
.filter-bar{ display:flex; gap:10px; flex-wrap:wrap; align-items:center; margin-bottom:24px; }
.filter-chip{
  font-family:'Space Grotesk',sans-serif; font-weight:600; font-size:13px; padding:8px 16px;
  border-radius:999px; border:1.5px solid var(--line); background:var(--white); cursor:pointer;
  text-decoration:none; color:var(--ink-soft);
}
.filter-chip:hover{ border-color:var(--ink); color:var(--ink); }
.filter-chip.active{ background:var(--ink); color:var(--white); border-color:var(--ink); }

.lesson-grid{ display:grid; grid-template-columns:repeat(auto-fill, minmax(300px, 1fr)); gap:18px; }
.lesson-card{ display:block; text-decoration:none; color:inherit; background:var(--white); border:1.5px solid var(--line); border-radius:var(--radius-lg); padding:22px; transition:transform .15s, box-shadow .15s; }
.lesson-card:hover{ transform:translateY(-3px); box-shadow:0 10px 24px rgba(22,19,17,0.1); border-color:var(--cobalt); }
.lesson-card .topic-tag{ font-family:'IBM Plex Mono',monospace; font-size:10.5px; letter-spacing:.8px; text-transform:uppercase; color:var(--copper); font-weight:700; margin-bottom:10px; display:block; }
.lesson-card h3{ font-family:'Space Grotesk',sans-serif; font-size:17px; margin-bottom:8px; }
.lesson-card p{ font-size:13.5px; color:var(--muted); line-height:1.6; }
.lesson-meta{ display:flex; align-items:center; justify-content:space-between; margin-top:14px; padding-top:12px; border-top:1px solid var(--line); font-size:12px; color:var(--ink-faint); }
.lesson-meta b{ color:var(--copper); }

/* Lesson detail */
.lesson-body{ max-width:820px; margin:0 auto; }
.lesson-body h1{ font-family:'Space Grotesk',sans-serif; font-size:28px; margin-bottom:10px; line-height:1.25; }
.lesson-body h2{ font-family:'Space Grotesk',sans-serif; font-size:20px; margin:26px 0 12px; }
.lesson-body h3{ font-family:'Space Grotesk',sans-serif; font-size:17px; margin:20px 0 10px; }
.lesson-body p{ font-size:15px; line-height:1.75; color:var(--ink-soft); margin-bottom:14px; }
.lesson-body ul, .lesson-body ol{ margin:0 0 14px 26px; color:var(--ink-soft); }
.lesson-body li{ font-size:15px; line-height:1.7; margin-bottom:6px; }
.lesson-body table{ width:100%; border-collapse:collapse; margin:14px 0; font-size:14px; }
.lesson-body th, .lesson-body td{ border:1.5px solid var(--line); padding:9px 12px; text-align:left; }
.lesson-body th{ background:var(--paper-2); }
.lesson-actions{ display:flex; gap:12px; flex-wrap:wrap; margin-top:30px; padding-top:22px; border-top:1.5px solid var(--line); }

/* Quiz taking */
.quiz-question{ background:var(--white); border:1.5px solid var(--line); border-radius:var(--radius-lg); padding:24px; margin-bottom:18px; }
.quiz-question .q-num{ font-family:'Space Mono'; font-size:12px; color:var(--copper); font-weight:700; margin-bottom:8px; }
.quiz-question h3{ font-family:'Space Grotesk',sans-serif; font-size:17px; margin-bottom:16px; line-height:1.4; }
.choice{ display:block; }
.choice input{ display:none; }
.choice .choice-label{
  display:flex; align-items:center; gap:12px; padding:12px 16px; border:1.5px solid var(--line);
  border-radius:var(--radius-sm); margin-bottom:9px; cursor:pointer; font-size:14.5px; transition:border-color .15s, background .15s;
}
.choice input:checked + .choice-label{ border-color:var(--cobalt); background:var(--sky-tint); font-weight:600; }
.choice .choice-letter{ width:26px; height:26px; border-radius:50%; background:var(--paper-2); display:flex; align-items:center; justify-content:center; font-family:'Space Mono'; font-weight:700; font-size:12px; flex-shrink:0; }
.choice input:checked + .choice-label .choice-letter{ background:var(--cobalt); color:#fff; }
.quiz-result{ background:var(--lab-night); color:#fff; border-radius:var(--radius-lg); padding:32px; text-align:center; margin-bottom:26px; }
.quiz-result .score-big{ font-family:'Space Mono'; font-size:54px; font-weight:700; color:var(--citrine); }
.quiz-result p{ color:#c8c2e8; margin:8px 0; }
.result-item{ background:var(--white); border:1.5px solid var(--line); border-radius:var(--radius); padding:16px 18px; margin-bottom:12px; }
.result-item.correct{ border-left:5px solid var(--chloro); }
.result-item.wrong{ border-left:5px solid var(--danger); }
.result-item .explanation{ font-size:13.5px; color:var(--ink-soft); margin-top:8px; line-height:1.55; }

/* ---------- Elements (Periodic table) ---------- */
.pt-controls{ display:flex; gap:10px; flex-wrap:wrap; align-items:center; margin-bottom:22px; }
.pt-search{ flex:1; min-width:200px; padding:11px 16px; border:1.5px solid var(--ink); border-radius:var(--radius-sm); font-size:14px; font-family:inherit; background:var(--white); }
.pt-search:focus{ outline:none; border-color:var(--cobalt); }
.periodic-table{ display:grid; grid-template-columns:repeat(18, 1fr); gap:5px; margin-bottom:36px; }
.pt-cell{
  aspect-ratio:1/0.95; border:1.5px solid var(--line); border-radius:8px; background:var(--white);
  display:flex; flex-direction:column; align-items:center; justify-content:center; cursor:pointer;
  text-decoration:none; color:inherit; transition:transform .12s, box-shadow .12s; padding:3px;
}
.pt-cell:hover{ transform:scale(1.18); z-index:5; box-shadow:0 6px 18px rgba(22,19,17,0.2); border-color:var(--ink); }
.pt-cell .z{ font-family:'Space Mono'; font-size:9px; color:var(--ink-faint); }
.pt-cell .sym{ font-family:'Space Grotesk',sans-serif; font-weight:700; font-size:clamp(12px,1.6vw,17px); line-height:1.1; }
.pt-cell .nm{ font-size:clamp(7px,0.9vw,9.5px); color:var(--muted); text-align:center; line-height:1.1; overflow:hidden; white-space:nowrap; text-overflow:ellipsis; max-width:100%; }
.pt-empty{ visibility:hidden; }
.pt-cell.cat-phi-kim{ background:var(--electron-tint); }
.pt-cell.cat-kim-loai-chuyen-tiep{ background:var(--chloro-tint); }
.pt-cell.cat-kim-loai-kiem{ background:var(--litmus-tint); }
.pt-cell.cat-kim-loai-kiem-tho{ background:var(--citrine-tint); }
.pt-cell.cat-halogen{ background:var(--sky-tint); }
.pt-cell.cat-khi-hiem{ background:#F1E9FF; }
.pt-cell.cat-a-kim{ background:#FFE4D8; }
.pt-cell.cat-kim-loai-yeu{ background:#E9F3EC; }
.pt-cell.cat-kim-loai-dat-hiem, .pt-cell.cat-kim-loai-actini{ background:#FDE8F0; }
.pt-cell.cat-khac{ background:var(--white); }

.element-detail{ max-width:720px; margin:0 auto; }
.element-hero{ display:flex; gap:24px; align-items:center; flex-wrap:wrap; }
.element-symbol-box{
  width:130px; height:140px; border:2px solid var(--ink); border-radius:var(--radius);
  display:flex; flex-direction:column; align-items:center; justify-content:center; box-shadow:var(--shadow-hard);
  background:var(--white); flex-shrink:0;
}
.element-symbol-box .z{ font-family:'Space Mono'; font-size:16px; color:var(--ink-faint); }
.element-symbol-box .sym{ font-family:'Space Grotesk',sans-serif; font-size:58px; font-weight:700; }
.element-symbol-box .nm{ font-size:12px; color:var(--ink-soft); }
.element-info h1{ font-family:'Space Grotesk',sans-serif; font-size:30px; margin-bottom:10px; }
.element-info .mass{ font-family:'Space Mono'; font-size:15px; color:var(--muted); }
.element-facts{ display:grid; grid-template-columns:repeat(auto-fit, minmax(150px,1fr)); gap:10px; margin:20px 0; }
.fact-box{ background:var(--paper-tint); border-radius:var(--radius-sm); padding:12px; }
.fact-box .k{ font-size:11px; color:var(--ink-faint); font-weight:700; text-transform:uppercase; letter-spacing:.5px; }
.fact-box .v{ font-weight:700; font-size:15px; margin-top:3px; }
.story-box{ background:var(--lab-night); color:#fff; border-radius:var(--radius); padding:22px; margin-top:18px; }
.story-box h3{ font-size:15px; margin-bottom:8px; color:var(--citrine); }
.story-box p{ font-size:14px; line-height:1.7; color:#d8d2ee; }
.fun-box{ background:var(--citrine-tint); border:1.5px solid var(--citrine); border-radius:var(--radius); padding:16px 20px; margin-top:14px; font-size:14px; line-height:1.6; }

/* ---------- AI Lab ---------- */
.ai-layout{ display:grid; grid-template-columns:260px 1fr; gap:18px; align-items:start; }
.ai-sidebar .card{ padding:16px; }
.ai-sidebar h3{ font-size:13px; text-transform:uppercase; letter-spacing:.8px; font-family:'IBM Plex Mono',monospace; color:var(--muted); margin-bottom:12px; }
.ai-sidebar a{ display:block; padding:10px 12px; border-radius:8px; font-size:13.5px; font-weight:600; color:var(--ink-soft); text-decoration:none; margin-bottom:4px; }
.ai-sidebar a:hover, .ai-sidebar a.active{ background:var(--paper-tint); color:var(--ink); }
.ai-sidebar a.new-chat{ background:var(--cobalt); color:#fff; margin-bottom:14px; }
.ai-sidebar a.new-chat:hover{ background:#2149A8; }

.chat-box{ background:var(--white); border:1.5px solid var(--line); border-radius:var(--radius-lg); display:flex; flex-direction:column; height:66vh; min-height:440px; overflow:hidden; }
.chat-header{ padding:14px 20px; border-bottom:1.5px solid var(--line); display:flex; align-items:center; justify-content:space-between; }
.chat-header .model-chip{ font-family:'Space Mono'; font-size:11px; background:var(--paper-2); padding:4px 10px; border-radius:999px; }
.chat-messages{ flex:1; overflow-y:auto; padding:20px; display:flex; flex-direction:column; gap:14px; }
.msg{ max-width:80%; padding:12px 16px; border-radius:var(--radius); font-size:14.5px; line-height:1.65; }
.msg.user{ align-self:flex-end; background:var(--cobalt); color:#fff; border-bottom-right-radius:4px; }
.msg.ai{ align-self:flex-start; background:var(--paper-2); color:var(--ink); border-bottom-left-radius:4px; }
.msg.ai b{ color:var(--ink); }
.msg .ai-code{ display:block; background:var(--lab-night); color:#c9f29a; padding:12px; border-radius:8px; font-family:'Space Mono'; font-size:12.5px; overflow-x:auto; margin:8px 0; white-space:pre; }
.msg .loading-dots{ display:inline-flex; gap:4px; }
.msg .loading-dots span{ width:7px; height:7px; border-radius:50%; background:var(--ink-faint); animation:bounce .9s infinite; }
.msg .loading-dots span:nth-child(2){ animation-delay:.15s; }
.msg .loading-dots span:nth-child(3){ animation-delay:.3s; }
@keyframes bounce{ 0%,80%,100%{ transform:translateY(0); } 40%{ transform:translateY(-6px); } }
.chat-input-area{ border-top:1.5px solid var(--line); padding:14px; display:flex; gap:10px; }
.chat-input-area textarea{
  flex:1; border:1.5px solid var(--line); border-radius:var(--radius-sm); padding:10px 12px;
  font-family:inherit; font-size:14px; resize:none; min-height:44px; max-height:120px; background:var(--paper);
}
.chat-input-area textarea:focus{ outline:none; border-color:var(--cobalt); }
.suggestion-chips{ padding:0 20px 12px; display:flex; gap:8px; flex-wrap:wrap; }
.suggestion-chips .chip-q{ font-size:12px; padding:6px 12px; border:1.5px solid var(--line); border-radius:999px; background:var(--paper); cursor:pointer; color:var(--ink-soft); }
.suggestion-chips .chip-q:hover{ border-color:var(--cobalt); color:var(--ink); }

/* ---------- Admin Panel ---------- */
.admin-wrap{ display:flex; min-height:100vh; background:#F6F4EE; }
.admin-sidebar{ width:240px; background:#17141F; color:#fff; padding:24px 0; flex-shrink:0; position:sticky; top:0; height:100vh; overflow-y:auto; }
.admin-sidebar .as-brand{ padding:0 22px 22px; border-bottom:1px solid rgba(255,255,255,.1); margin-bottom:12px; }
.admin-sidebar .as-brand b{ font-family:'Space Grotesk',sans-serif; font-size:16px; display:block; }
.admin-sidebar .as-brand small{ color:#9a94ad; font-size:11px; }
.admin-sidebar a{ display:flex; align-items:center; gap:10px; padding:11px 22px; color:#b9b3c9; font-size:13.5px; font-weight:600; text-decoration:none; }
.admin-sidebar a:hover{ background:rgba(255,255,255,.06); color:#fff; }
.admin-sidebar a.active{ background:rgba(108,76,241,.25); color:#fff; border-left:3px solid var(--electron); }
.admin-main{ flex:1; padding:28px 32px; min-width:0; }
.admin-head{ display:flex; align-items:center; justify-content:space-between; flex-wrap:wrap; gap:12px; margin-bottom:24px; }
.admin-head h1{ font-family:'Space Grotesk',sans-serif; font-size:24px; }
.admin-page-desc{ color:#6b6578; font-size:14px; margin-bottom:20px; }

.stat-grid{ display:grid; grid-template-columns:repeat(auto-fit, minmax(180px,1fr)); gap:14px; margin-bottom:26px; }
.stat-card{ background:#fff; border:1px solid #E5E1D6; border-radius:14px; padding:18px; }
.stat-card .sv{ font-family:'Space Mono'; font-size:26px; font-weight:700; }
.stat-card .sl{ font-size:12px; color:#6b6578; font-weight:700; margin-top:4px; }
.stat-card.accent{ background:var(--electron); color:#fff; border:none; }
.stat-card.accent .sl{ color:rgba(255,255,255,.75); }

.admin-table{ width:100%; border-collapse:collapse; background:#fff; border:1px solid #E5E1D6; border-radius:12px; overflow:hidden; }
.admin-table th{ background:#F1EEE4; text-align:left; font-size:12px; text-transform:uppercase; letter-spacing:.5px; color:#6b6578; padding:12px 14px; }
.admin-table td{ padding:12px 14px; font-size:14px; border-top:1px solid #EFECE2; vertical-align:middle; }
.admin-table tr:hover td{ background:#FBF9F3; }
.tag-pill{ display:inline-block; font-size:11px; font-weight:700; padding:3px 10px; border-radius:999px; }
.tag-pill.success{ background:var(--chloro-tint); color:var(--chloro); }
.tag-pill.warn{ background:var(--citrine-tint); color:#A37400; }
.tag-pill.danger{ background:#FDE8E8; color:var(--danger); }
.tag-pill.info{ background:var(--sky-tint); color:var(--sky); }
.tag-pill.mono{ font-family:'Space Mono',monospace; }

.action-row{ display:flex; gap:6px; }
.btn-xs{ padding:5px 10px; font-size:12px; border-radius:8px; border:1px solid #D9D4C6; background:#fff; cursor:pointer; font-weight:600; color:#444; text-decoration:none; display:inline-block; }
.btn-xs:hover{ border-color:#444; }
.btn-xs.danger{ color:var(--danger); }
.btn-xs.danger:hover{ background:#FDE8E8; border-color:var(--danger); }

/* Admin form panel */
.form-panel{ background:#fff; border:1px solid #E5E1D6; border-radius:14px; padding:24px; margin-bottom:24px; }
.form-panel h3{ font-family:'Space Grotesk',sans-serif; font-size:16px; margin-bottom:16px; }
.form-row{ display:grid; grid-template-columns:1fr 1fr; gap:16px; }
.form-panel .form-control{ border:1px solid #D9D4C6; border-radius:8px; background:#FAF8F2; }
.form-panel label{ font-size:13px; font-weight:600; color:#4a4552; }
.switch-row{ display:flex; align-items:center; gap:12px; padding:10px 0; }
.switch{ position:relative; width:42px; height:24px; flex-shrink:0; }
.switch input{ opacity:0; width:0; height:0; }
.switch .slider{ position:absolute; inset:0; background:#D9D4C6; border-radius:999px; cursor:pointer; transition:.2s; }
.switch .slider::before{ content:''; position:absolute; width:18px; height:18px; left:3px; top:3px; background:#fff; border-radius:50%; transition:.2s; }
.switch input:checked + .slider{ background:var(--chloro); }
.switch input:checked + .slider::before{ transform:translateX(18px); }

/* Toggle list (AI models) */
.model-list{ display:flex; flex-direction:column; gap:8px; }
.model-item{ display:flex; align-items:center; gap:14px; background:#fff; border:1px solid #E5E1D6; border-radius:10px; padding:12px 16px; }
.model-item .mi-name{ flex:1; }
.model-item .mi-name b{ font-size:14px; display:block; }
.model-item .mi-name small{ color:#6b6578; font-size:12px; font-family:'Space Mono',monospace; }

.pagination{ display:flex; gap:6px; margin-top:20px; justify-content:center; }
.pagination a, .pagination span{ padding:7px 12px; border-radius:8px; font-size:13px; font-weight:600; border:1px solid #D9D4C6; background:#fff; text-decoration:none; color:#444; }
.pagination .current{ background:var(--ink); color:#fff; border-color:var(--ink); }

/* ---------- Responsive ---------- */
@media(max-width:960px){
  .feature-grid{ grid-template-columns:repeat(2,1fr); }
  .dash-grid{ grid-template-columns:1fr; }
  .span-2{ grid-column:auto; }
  .ai-layout{ grid-template-columns:1fr; }
  .footer-grid{ grid-template-columns:1fr; gap:22px; }
  .form-row{ grid-template-columns:1fr; }
  .periodic-table{ grid-template-columns:repeat(9, 1fr); }
  .admin-sidebar{ width:100%; height:auto; position:relative; }
  .admin-wrap{ flex-direction:column; }
}
@media(max-width:680px){
  .level-grid{ grid-template-columns:1fr; }
  .feature-grid{ grid-template-columns:1fr; }
  .main-nav{ display:none; width:100%; flex-direction:column; gap:2px; }
  .nav-open .main-nav{ display:flex; }
  .menu-toggle{ display:block; }
  .header-cta .link-btn{ display:none; }
  .quick-grid{ grid-template-columns:repeat(2,1fr); }
  .lb-podium{ grid-template-columns:1fr; }
  .podium-card.first{ transform:none; }
}

/* ---------- News / Content prose ---------- */
.prose{ line-height:1.75; font-size:15px; }
.prose p{ margin-bottom:12px; }
.prose b{ background:var(--citrine-tint); padding:0 3px; border-radius:4px; }
.prose pre.ai-code{ background:var(--lab-night); color:#E9E3FF; padding:14px; border-radius:var(--radius-sm); border:2.5px solid var(--ink); box-shadow:3px 3px 0 var(--ink); overflow-x:auto; font-family:'IBM Plex Mono',monospace; font-size:13px; margin:12px 0; }

/* ---------- Notifications ---------- */
.notif-item{ transition:transform .12s ease, box-shadow .12s ease; }
.notif-item:hover{ transform:translate(-2px,-2px); box-shadow:var(--shadow-hard); }