/* =========================================================================
 * Vật Lý Pro THPT — giao diện chính
 * ========================================================================= */
:root{
  --navy:#0c2a6b;--navy-2:#123a8f;--ink:#0f1b3d;--text:#1e2a4a;--muted:#5b6b8f;--line:#dbe3f5;
  --bg:#f3f6fd;--card:#fff;--cyan:#06b6d4;--blue:#2563eb;--amber:#f59e0b;--green:#10b981;--red:#ef4444;--purple:#7c3aed;
  --g10:#2563eb;--g11:#7c3aed;--g12:#db2777;
  --r:16px;--shadow:0 1px 2px rgba(15,27,61,.06),0 8px 24px -12px rgba(15,27,61,.18);
  --shadow-lg:0 20px 50px -20px rgba(12,42,107,.45);
}
*{box-sizing:border-box}
html{-webkit-text-size-adjust:100%;scroll-behavior:smooth;scroll-padding-top:80px}
body{margin:0;font-family:"Be Vietnam Pro",system-ui,-apple-system,"Segoe UI",Roboto,sans-serif;color:var(--text);background:var(--bg);line-height:1.6;font-size:16px;overflow-x:hidden}
img{max-width:100%;height:auto}
a{color:var(--blue);text-decoration:none}a:hover{text-decoration:underline}
h1,h2,h3{color:var(--ink);line-height:1.25;margin:0 0 .5em;letter-spacing:-.01em}
h1{font-size:clamp(1.7rem,3.6vw,2.4rem);font-weight:800}
h2{font-size:clamp(1.25rem,2.4vw,1.55rem);font-weight:800}
h3,.h3{font-size:1.1rem;font-weight:700}
p{margin:0 0 1em}
kbd{background:#fff;border:1px solid var(--line);border-bottom-width:2px;border-radius:6px;padding:1px 6px;font:600 .85em ui-monospace,monospace}
.wrap{max-width:1180px;margin:0 auto;padding:0 20px}
.page{padding-top:22px;padding-bottom:56px;min-height:60vh}
.narrow{max-width:520px}
.muted{color:var(--muted)}.small{font-size:.88rem}
.visually-hidden{position:absolute!important;width:1px;height:1px;overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap}
.skip{position:absolute;left:-999px;top:8px;background:#fff;padding:8px 14px;border-radius:8px;z-index:100}.skip:focus{left:8px}
:focus-visible{outline:3px solid #38bdf8;outline-offset:2px}

/* nền kí hiệu bay */
.bg-symbols{position:fixed;inset:0;pointer-events:none;z-index:-1;overflow:hidden}
.bg-symbols span{position:absolute;font-weight:800;color:rgba(37,99,235,.055);font-size:46px;white-space:nowrap;animation:floaty 26s ease-in-out infinite}
.bg-symbols span:nth-child(1){left:4%;top:12%}.bg-symbols span:nth-child(2){left:82%;top:8%;font-size:70px}.bg-symbols span:nth-child(3){left:66%;top:62%}
.bg-symbols span:nth-child(4){left:12%;top:70%;font-size:64px}.bg-symbols span:nth-child(5){left:44%;top:30%}.bg-symbols span:nth-child(6){left:90%;top:42%}
.bg-symbols span:nth-child(7){left:28%;top:88%}.bg-symbols span:nth-child(8){left:56%;top:4%;font-size:60px}.bg-symbols span:nth-child(9){left:2%;top:40%}
.bg-symbols span:nth-child(10){left:74%;top:84%}.bg-symbols span:nth-child(11){left:36%;top:56%}.bg-symbols span:nth-child(12){left:92%;top:72%;font-size:60px}
@keyframes floaty{0%,100%{transform:translateY(0) rotate(0)}50%{transform:translateY(-24px) rotate(4deg)}}
@media (prefers-reduced-motion:reduce){*{animation:none!important;transition:none!important;scroll-behavior:auto!important}}

/* ---------- Thanh trên ---------- */
.topbar{position:sticky;top:0;z-index:50;background:rgba(12,42,107,.97);backdrop-filter:saturate(1.4) blur(8px);color:#fff;box-shadow:0 6px 20px -12px rgba(0,0,0,.5)}
.topbar-in{display:flex;align-items:center;gap:14px;height:64px;max-width:1380px}
.brand{display:flex;align-items:center;gap:9px;color:#fff;text-decoration:none!important;flex-shrink:0}
.brand img{width:40px;height:40px}
.brand span{display:flex;flex-direction:column;line-height:1.05}
.brand b{font-size:1.15rem;font-weight:800;letter-spacing:-.01em}
.brand small{font-size:.68rem;font-weight:700;letter-spacing:.24em;color:#7dd3fc}
.mainnav{display:flex;gap:2px;margin-left:8px;flex:1;flex-wrap:nowrap;overflow:hidden}
.mainnav a{color:#dbe7ff;padding:8px 9px;border-radius:10px;font-weight:600;font-size:.9rem;white-space:nowrap;text-decoration:none}
.mainnav a:hover{background:rgba(255,255,255,.1);color:#fff}
.mainnav a.on{background:rgba(125,211,252,.18);color:#fff;box-shadow:inset 0 -2px 0 #7dd3fc}
.acct{display:flex;align-items:center;gap:8px;margin-left:auto}
.acct form.inline{display:inline}
.sound{background:transparent;border:0;color:#fff;font-size:1.15rem;cursor:pointer;padding:6px;border-radius:8px}
.sound:hover{background:rgba(255,255,255,.1)}
.sound[aria-pressed=false]{opacity:.55}
.me{display:flex;align-items:center;gap:7px;color:#fff;text-decoration:none!important;background:rgba(255,255,255,.08);border-radius:999px;padding:4px 12px 4px 4px;max-width:200px}
.me-lv{background:linear-gradient(135deg,#fbbf24,#f59e0b);color:#3a2300;font-weight:800;font-size:.75rem;border-radius:999px;padding:3px 8px}
.me-name{overflow:hidden;text-overflow:ellipsis;white-space:nowrap;font-weight:600;font-size:.9rem}
.nav-toggle{display:none;background:transparent;border:1px solid rgba(255,255,255,.3);color:#fff;font-size:1.3rem;border-radius:10px;width:42px;height:40px;cursor:pointer;margin-left:auto}
.topbar .btn-ghost{color:#fff;border-color:rgba(255,255,255,.35);background:transparent}
.topbar .btn-ghost:hover{background:rgba(255,255,255,.1)}
@media (max-width:1320px){
  .nav-toggle{display:block}
  .mainnav{position:absolute;left:0;right:0;top:64px;background:var(--navy);flex-direction:column;padding:10px 16px 16px;gap:2px;display:none;margin:0;box-shadow:0 20px 30px -10px rgba(0,0,0,.4)}
  .mainnav.open{display:flex}
  .mainnav a{padding:12px 12px;font-size:1rem}
  .acct{margin-left:0}
}
@media (max-width:560px){
  .topbar-in{gap:8px}
  .acct .btn-sm{padding:6px 10px;font-size:.82rem}
  .acct .btn-ghost.btn-sm{display:none}
  .me-name{display:none}.me{padding:4px}
  .brand b{font-size:1.02rem}
}

/* ---------- Nút ---------- */
.btn{display:inline-flex;align-items:center;justify-content:center;gap:6px;border-radius:12px;padding:10px 18px;font:700 .95rem/1.2 "Be Vietnam Pro",system-ui,sans-serif;border:1.5px solid transparent;cursor:pointer;text-decoration:none!important;transition:transform .08s,box-shadow .15s,background .15s;white-space:nowrap}
.btn:active{transform:translateY(1px)}
.btn-primary{background:linear-gradient(180deg,#2f6bf2,#1d4ed8);color:#fff;box-shadow:0 6px 16px -6px rgba(29,78,216,.7)}
.btn-primary:hover{box-shadow:0 10px 22px -8px rgba(29,78,216,.85)}
.btn-accent{background:linear-gradient(180deg,#fbbf24,#f59e0b);color:#3a2300;box-shadow:0 6px 16px -6px rgba(245,158,11,.7)}
.btn-ghost{background:#fff;color:var(--navy);border-color:var(--line)}
.btn-ghost:hover{border-color:#a9bbe6}
.btn-sm{padding:7px 12px;font-size:.86rem;border-radius:10px}
.btn-lg{padding:14px 24px;font-size:1.05rem;border-radius:14px}
.btn-block{display:flex;width:100%}
.btn[disabled]{opacity:.6;cursor:not-allowed}

/* ---------- Khung chung ---------- */
.card{background:var(--card);border:1px solid var(--line);border-radius:var(--r);box-shadow:var(--shadow);color:var(--text);text-decoration:none!important;display:block;transition:transform .15s,box-shadow .15s,border-color .15s}
a.card:hover{transform:translateY(-3px);box-shadow:var(--shadow-lg);border-color:#b8c8ee}
.pad{padding:20px}
.sec{margin-top:40px}
.sec-head{display:flex;align-items:baseline;justify-content:space-between;gap:12px;flex-wrap:wrap;margin-bottom:14px}
.sec-head .sec-title{margin:0}
.sec-head a{font-weight:600}
.sec-title{font-size:1.35rem;margin-bottom:14px}
.two-col{display:grid;grid-template-columns:1fr 1fr;gap:28px}
.two-col>*{min-width:0}
@media (max-width:860px){.two-col{grid-template-columns:1fr}}
.stack{display:flex;flex-direction:column;gap:12px}
.empty{background:#fff;border:1.5px dashed var(--line);border-radius:var(--r);padding:22px;text-align:center;color:var(--muted)}
.chips{display:flex;gap:5px;flex-wrap:wrap}
.chip{display:inline-block;align-self:flex-start;font-style:normal;font-size:.72rem;font-weight:700;padding:2px 8px;border-radius:999px;background:#e8eefc;color:var(--navy)}
.chip-10{background:#dbeafe;color:#1d4ed8}.chip-11{background:#ede9fe;color:#6d28d9}.chip-12{background:#fce7f3;color:#be185d}
.crumbs{font-size:.88rem;color:var(--muted);margin-bottom:14px;display:flex;flex-wrap:wrap;gap:4px;align-items:center}
.crumbs b{color:var(--ink);font-weight:600}
.phead{margin-bottom:22px}
.phead .lead,.lead{font-size:1.06rem;color:#3e4d72;max-width:820px}
.eyebrow{text-transform:uppercase;letter-spacing:.12em;font-size:.76rem;font-weight:800;color:var(--blue);margin:0 0 6px}
.tabs{display:flex;gap:6px;flex-wrap:wrap;margin:0 0 18px}
.tabs a{padding:8px 16px;border-radius:999px;background:#fff;border:1px solid var(--line);font-weight:600;color:var(--text);text-decoration:none}
.tabs a.on{background:var(--navy);color:#fff;border-color:var(--navy)}
.tabs-sm a{padding:5px 12px;font-size:.88rem}
.alert{background:#fef2f2;color:#991b1b;border:1px solid #fecaca;border-radius:12px;padding:12px 14px;margin:0 0 16px}
.alert.ok{background:#ecfdf5;color:#065f46;border-color:#a7f3d0}
.note-guest{background:#fffbeb;border:1px solid #fde68a;color:#78350f;border-radius:12px;padding:10px 14px;font-size:.92rem}

/* ---------- Trang chủ ---------- */
.hero{display:grid;grid-template-columns:1.25fr 1fr;gap:30px;align-items:center;background:radial-gradient(1200px 400px at 90% -10%,#1e5fd8 0,transparent 60%),linear-gradient(135deg,#0c2a6b 0%,#0e1f4f 60%,#1a1150 100%);color:#e6eeff;border-radius:28px;padding:44px 44px 36px;position:relative;overflow:hidden;box-shadow:var(--shadow-lg)}
.hero::after{content:"";position:absolute;inset:0;background-image:linear-gradient(rgba(125,211,252,.07) 1px,transparent 1px),linear-gradient(90deg,rgba(125,211,252,.07) 1px,transparent 1px);background-size:36px 36px;mask-image:radial-gradient(circle at 70% 40%,#000,transparent 75%);pointer-events:none}
.hero h1{color:#fff;font-size:clamp(2rem,4.6vw,3.2rem);line-height:1.1;margin-bottom:16px}
.hero .grad{background:linear-gradient(90deg,#7dd3fc,#fbbf24);-webkit-background-clip:text;background-clip:text;color:transparent}
.hero .lead{color:#c7d6f7}
.hero .eyebrow{color:#7dd3fc}
.hero-text{position:relative;z-index:1}
.hero-cta{display:flex;gap:10px;flex-wrap:wrap;margin:22px 0 26px}
.hero .btn-ghost{background:rgba(255,255,255,.08);color:#fff;border-color:rgba(255,255,255,.3)}
.stats{display:flex;gap:26px;list-style:none;padding:0;margin:0;flex-wrap:wrap}
.stats li{display:flex;flex-direction:column;font-size:.85rem;color:#a9bde8}
.stats b{font-size:1.6rem;color:#fff;font-weight:800;line-height:1.1}
.hero-art{position:relative;height:340px;display:grid;place-items:center;z-index:1}
.hero-art img{width:200px;height:200px;position:relative;z-index:2;filter:drop-shadow(0 18px 30px rgba(0,0,0,.45));animation:bob 5s ease-in-out infinite}
@keyframes bob{50%{transform:translateY(-10px)}}
.orbit{position:absolute;border:1.5px dashed rgba(125,211,252,.35);border-radius:50%;animation:spin linear infinite}
.orbit i{position:absolute;top:-7px;left:50%;width:14px;height:14px;border-radius:50%;background:#fbbf24;box-shadow:0 0 16px #fbbf24}
.o1{width:250px;height:250px;animation-duration:9s}.o2{width:320px;height:180px;animation-duration:14s;animation-direction:reverse}.o2 i{background:#22d3ee;box-shadow:0 0 16px #22d3ee}
.o3{width:180px;height:320px;animation-duration:18s}.o3 i{background:#f472b6;box-shadow:0 0 16px #f472b6}
@keyframes spin{to{transform:rotate(360deg)}}
.bubble{position:absolute;background:rgba(255,255,255,.1);border:1px solid rgba(255,255,255,.25);backdrop-filter:blur(4px);color:#fff;font-weight:700;padding:6px 12px;border-radius:999px;font-size:.92rem;z-index:3;animation:bob 6s ease-in-out infinite}
.b1{top:8%;left:2%}.b2{top:16%;right:0;animation-delay:-2s}.b3{bottom:14%;left:0;animation-delay:-4s}.b4{bottom:6%;right:6%;animation-delay:-1s}
@media (max-width:860px){.hero{grid-template-columns:1fr;padding:30px 22px}.hero-art{height:220px;order:-1}.hero-art img{width:130px;height:130px}.o1{width:170px;height:170px}.o2{width:230px;height:130px}.o3{width:130px;height:220px}}
@media (max-width:480px){.stats{gap:16px}.stats b{font-size:1.3rem}.hero-cta .btn-lg{width:100%}}

.grade-grid{display:grid;grid-template-columns:repeat(3,1fr);gap:16px}
.grade-card{display:flex;flex-direction:column;gap:4px;padding:22px;border-radius:20px;color:#fff!important;text-decoration:none!important;position:relative;overflow:hidden;box-shadow:var(--shadow);transition:transform .15s}
.grade-card:hover{transform:translateY(-4px)}
.grade-card b{font-size:1.35rem;font-weight:800}
.grade-card span{opacity:.92;font-size:.92rem}
.grade-card .gr-icon{font-size:2.4rem;opacity:1;line-height:1.2}
.grade-card.g10{background:linear-gradient(135deg,#2563eb,#0ea5e9)}.grade-card.g11{background:linear-gradient(135deg,#7c3aed,#c026d3)}.grade-card.g12{background:linear-gradient(135deg,#db2777,#f97316)}
@media (max-width:760px){.grade-grid{grid-template-columns:1fr}}

.try-sim{display:grid;grid-template-columns:.8fr 1.6fr;gap:26px;align-items:center}
.try-sim .sim{margin:0}
@media (max-width:900px){.try-sim{grid-template-columns:1fr}}

.feature-grid{display:grid;grid-template-columns:repeat(4,1fr);gap:16px}
.feature{background:#fff;border:1px solid var(--line);border-radius:var(--r);padding:20px;color:var(--text);text-decoration:none!important;box-shadow:var(--shadow);transition:transform .15s}
.feature:hover{transform:translateY(-3px)}
.feature span{font-size:2rem}.feature b{display:block;font-size:1.05rem;color:var(--ink);margin:6px 0}.feature p{margin:0;color:var(--muted);font-size:.92rem}
@media (max-width:900px){.feature-grid{grid-template-columns:1fr 1fr}}
@media (max-width:480px){.feature-grid{grid-template-columns:1fr}}
.seo-text{background:#fff;border-radius:var(--r);padding:24px;border:1px solid var(--line);color:#3e4d72}
.seo-text h2{font-size:1.15rem}

/* lưới thẻ */
.game-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(330px,1fr));gap:14px}
.game-card{display:flex;align-items:center;gap:14px;padding:16px}
.gc-icon{font-size:2rem;width:56px;height:56px;border-radius:16px;background:linear-gradient(135deg,#eef4ff,#e0e9ff);display:grid;place-items:center;flex-shrink:0}
.gc-body{display:flex;flex-direction:column;gap:4px;min-width:0;flex:1}
.gc-body b{color:var(--ink);font-size:1rem}
.gc-body>span:not(.chips){font-size:.86rem;color:var(--muted);line-height:1.4}
.gc-play{width:34px;height:34px;border-radius:50%;background:var(--navy);color:#fff;display:grid;place-items:center;font-size:.8rem;flex-shrink:0}
.game-mini{display:flex;align-items:center;gap:12px;padding:12px 16px}.game-mini b{flex:1;color:var(--ink)}.game-mini>span:first-child{font-size:1.5rem}

.lesson-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:14px}
.lesson-card{display:flex;flex-direction:column;gap:6px;padding:18px}
.lc-top{display:flex;justify-content:space-between;align-items:center}
.lc-icon{font-size:1.6rem}
.lesson-card b{color:var(--ink);font-size:1.02rem;line-height:1.35}
.lesson-card>span:not(.lc-top):not(.lc-sim){font-size:.88rem;color:var(--muted);line-height:1.45}
.lc-sim{font-size:.8rem;font-weight:700;color:var(--cyan);margin-top:auto}

.sim-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(300px,1fr));gap:16px}
.sim-card{overflow:hidden;display:flex;flex-direction:column}
.sc-thumb{position:relative;aspect-ratio:16/9;background:linear-gradient(135deg,#0e1b3d,#16306b);display:grid;place-items:center;overflow:hidden}
.sc-thumb img{position:absolute;inset:0;width:100%;height:100%;object-fit:cover}
.sc-icon{font-size:2.6rem;filter:drop-shadow(0 6px 10px rgba(0,0,0,.4))}
.sc-thumb img+.sc-icon{position:absolute;right:10px;bottom:8px;font-size:1.5rem;background:rgba(11,22,48,.75);border-radius:10px;padding:2px 6px}
.sc-body{padding:14px 16px 16px;display:flex;flex-direction:column;gap:5px}
.sc-body b{color:var(--ink);line-height:1.3}
.sc-body>span{font-size:.86rem;color:var(--muted);line-height:1.45}
.sim-big{margin-top:0}

.mm-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:14px}
.mm-card{padding:18px;display:flex;flex-direction:column;gap:6px;border-top:4px solid var(--g10)}
.mm-card.g11{border-top-color:var(--g11)}.mm-card.g12{border-top-color:var(--g12)}
.mm-card b{color:var(--ink);font-size:1.05rem}.mm-card span{font-size:.86rem;color:var(--muted)}

.cta-row{display:flex;gap:10px;flex-wrap:wrap}

/* bảng */
.tbl{width:100%;border-collapse:separate;border-spacing:0;background:#fff;border:1px solid var(--line);border-radius:14px;overflow:hidden;font-size:.94rem}
.tbl th,.tbl td{padding:10px 12px;text-align:left;border-bottom:1px solid #edf1fa;vertical-align:top}
.tbl th{background:#f2f6ff;color:var(--navy);font-weight:700;font-size:.85rem}
.tbl tr:last-child td{border-bottom:0}
.tbl tr.me td{background:#fffbeb}
.rank td:first-child{width:46px;font-weight:700;text-align:center}
.prose .tbl,.lesson-body .tbl{margin:12px 0}
@media (max-width:700px){.prose .tbl,.lesson-body .tbl{display:block;overflow-x:auto}}
.podium{list-style:none;padding:0;margin:0;display:flex;flex-direction:column;gap:8px}
.podium li{display:flex;align-items:center;gap:10px;background:#fff;border:1px solid var(--line);border-radius:12px;padding:10px 14px}
.podium .medal{width:28px;text-align:center;font-weight:800;color:var(--muted)}
.podium b{flex:1;color:var(--ink);overflow:hidden;text-overflow:ellipsis;white-space:nowrap}
.podium .pts{font-weight:800;color:var(--navy)}

/* giải đấu */
.tour-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(300px,1fr));gap:14px}
.tour-card{padding:18px;display:flex;flex-direction:column;gap:6px;border-left:5px solid var(--amber)}
.tour-card.ended{border-left-color:#94a3b8;opacity:.85}.tour-card.soon{border-left-color:var(--cyan)}
.tour-card b{font-size:1.08rem;color:var(--ink)}
.prize{font-weight:700;color:#b45309;font-size:.9rem}
.badge-st{display:inline-block;align-self:flex-start;font-size:.72rem;font-weight:800;padding:3px 10px;border-radius:999px;text-transform:uppercase;letter-spacing:.06em}
.badge-st.live{background:#dcfce7;color:#15803d}.badge-st.soon{background:#cffafe;color:#0e7490}.badge-st.ended{background:#e2e8f0;color:#475569}
.tour-head{background:#fff;border:1px solid var(--line);border-radius:20px;padding:24px;box-shadow:var(--shadow)}
.tour-meta{list-style:none;padding:0;display:flex;gap:18px;flex-wrap:wrap;margin:6px 0 0;font-weight:600;color:#3e4d72}
.countdown{margin-top:12px;font-size:1.05rem;color:var(--navy)}
.me-rank{background:#eff6ff;border-radius:12px;padding:10px 14px}

/* ---------- Bài học ---------- */
.lesson-head{display:flex;gap:18px;align-items:flex-start;padding:26px;border-radius:22px;color:#fff;margin-bottom:24px;box-shadow:var(--shadow-lg)}
.lesson-head h1{color:#fff}.lesson-head .lead{color:rgba(255,255,255,.9);margin:0}.lesson-head .eyebrow{color:rgba(255,255,255,.8)}
.lesson-head.g10{background:linear-gradient(135deg,#1d4ed8,#0891b2)}.lesson-head.g11{background:linear-gradient(135deg,#6d28d9,#a21caf)}.lesson-head.g12{background:linear-gradient(135deg,#be185d,#ea580c)}
.lh-icon{font-size:2.8rem;background:rgba(255,255,255,.15);border-radius:18px;width:72px;height:72px;display:grid;place-items:center;flex-shrink:0}
.lesson-layout{display:grid;grid-template-columns:230px 1fr;gap:28px;align-items:start}
.toc{position:sticky;top:84px;background:#fff;border:1px solid var(--line);border-radius:var(--r);padding:16px;font-size:.9rem}
.toc ol{padding-left:18px;margin:8px 0 14px}.toc li{margin:4px 0}.toc a{color:var(--text)}
.lesson-body{min-width:0}
.lesson-body>section{margin-bottom:34px}
.lesson-body h2{padding-bottom:8px;border-bottom:2px solid #e3eafb}
.prose ul,.prose ol{padding-left:22px}.prose li{margin:4px 0}
.note{background:#eff6ff;border-left:4px solid var(--blue);border-radius:0 12px 12px 0;padding:12px 16px;margin:14px 0}
.note.warn,.note.canh-bao{background:#fffbeb;border-left-color:var(--amber)}
.note.tip,.note.meo{background:#ecfdf5;border-left-color:var(--green)}
.try-box{background:linear-gradient(135deg,#ecfeff,#eff6ff);border:1px solid #bae6fd;border-radius:var(--r);padding:16px 20px}
.try-box ul{margin:8px 0 0;padding-left:20px}.try-box li{margin:6px 0}
.formula-list{display:grid;grid-template-columns:repeat(auto-fill,minmax(300px,1fr));gap:12px}
.formula{background:#fff;border:1px solid var(--line);border-radius:14px;padding:12px 16px;display:flex;flex-direction:column;gap:2px}
.f-name{font-weight:700;color:var(--navy);font-size:.9rem}
.f-tex{overflow-x:auto;overflow-y:hidden;font-size:1.05rem}.f-tex .katex-display{margin:.4em 0}
.f-vars{font-size:.82rem;color:var(--muted);line-height:1.45}
.example{background:#fff;border:1px solid var(--line);border-radius:14px;padding:16px 18px;margin-bottom:12px}
.example details summary{cursor:pointer;font-weight:700;color:var(--blue);margin-top:4px}
.ex-steps{margin:10px 0;padding-left:22px}.ex-steps li{margin:6px 0}
.ex-ans{font-weight:700;color:#047857;margin:0}
.mistakes{list-style:none;padding:0}.mistakes li{background:#fff7ed;border:1px solid #fed7aa;border-radius:12px;padding:10px 14px 10px 40px;margin-bottom:8px;position:relative}
.mistakes li::before{content:"✗";position:absolute;left:14px;top:9px;color:#dc2626;font-weight:800}
.pager{display:grid;grid-template-columns:1fr 1fr;gap:14px;margin-top:30px}
.pager .card{padding:14px 18px}.pager .right{text-align:right}.pager small{display:block;color:var(--muted)}.pager b{color:var(--ink)}
.katex-display{overflow-x:auto;overflow-y:hidden;padding:2px 0}
/* giọng đọc Trúc Ly */
.btn-read{margin-top:14px;background:rgba(255,255,255,.16);color:#fff;border-color:rgba(255,255,255,.4)}
.btn-read:hover{background:rgba(255,255,255,.26)}
.btn-read[aria-pressed=true]{background:#fff;color:var(--navy)}
.sec-read{vertical-align:middle;margin-left:4px;width:32px;height:32px;border-radius:50%;border:1px solid var(--line);background:#fff;font-size:.9rem;line-height:1;cursor:pointer;opacity:.7;transition:opacity .15s,transform .15s}
.sec-read:hover,.sec-read:focus-visible{opacity:1;transform:scale(1.08)}
.sec-read[aria-pressed=true]{opacity:1;background:#eff6ff;border-color:var(--blue)}
.lesson-body>section.reading{box-shadow:-4px 0 0 0 #fbbf24;padding-left:14px;transition:box-shadow .2s,padding .2s}
@media (max-width:900px){.lesson-layout{grid-template-columns:1fr}.toc{position:static}.toc ol{columns:2}}
@media (max-width:560px){.lesson-head{flex-direction:column;padding:20px}.lh-icon{width:56px;height:56px;font-size:2rem}.toc ol{columns:1}.pager{grid-template-columns:1fr}.formula-list{grid-template-columns:1fr}}

.f-search{margin-bottom:14px}
.f-search input{width:100%;font:500 1rem "Be Vietnam Pro",system-ui,sans-serif;padding:14px 18px;border:1.5px solid var(--line);border-radius:14px;background:#fff}
.f-search input:focus{border-color:var(--blue);outline:none;box-shadow:0 0 0 4px rgba(37,99,235,.12)}
.f-group{margin-bottom:22px}.f-group h3 a{color:var(--ink)}

/* sơ đồ tư duy */
.mm-wrap{position:relative;background:#fff;border:1px solid var(--line);border-radius:20px;box-shadow:var(--shadow);overflow:hidden}
.mm-tools{position:absolute;top:10px;right:10px;z-index:2;display:flex;gap:6px;flex-wrap:wrap}
.mm-view{height:min(72vh,680px);overflow:hidden;cursor:grab;touch-action:none;background:radial-gradient(circle,#e6ecfa 1px,transparent 1px) 0 0/22px 22px}
.mm-view:active{cursor:grabbing}
.mm-view svg{transform-origin:0 0;display:block}
.mm-n.has-kids{cursor:pointer}
.mm-n.collapsed .mm-dot{fill:currentColor}
.mm-outline ul{padding-left:20px;margin:4px 0}

/* ---------- Trò chơi ---------- */
.game{background:linear-gradient(160deg,#0c2a6b,#151a4d);color:#e6eeff;border-radius:26px;padding:28px;min-height:440px;position:relative;overflow:hidden;box-shadow:var(--shadow-lg)}
.game h2,.game h3{color:#fff}
.game-intro{text-align:center;max-width:620px;margin:0 auto;display:flex;flex-direction:column;align-items:center;gap:10px}
.gi-icon{font-size:3.6rem;filter:drop-shadow(0 10px 20px rgba(0,0,0,.4))}
.game-intro h2{font-size:1.9rem;margin:0}
.game-intro p{color:#c7d6f7;margin:0}
.gi-rules{list-style:none;padding:0;margin:8px 0;display:flex;flex-direction:column;gap:6px;color:#dbe7ff}
.grade-pick{display:flex;gap:8px;flex-wrap:wrap;justify-content:center;margin:6px 0}
.grade-pick input{position:absolute;opacity:0;pointer-events:none}
.grade-pick span{display:inline-block;padding:8px 16px;border-radius:999px;border:1.5px solid rgba(255,255,255,.3);cursor:pointer;font-weight:600}
.grade-pick input:checked+span{background:#fbbf24;color:#3a2300;border-color:#fbbf24}
.grade-pick input:focus-visible+span{outline:3px solid #38bdf8}
.game .note-guest{background:rgba(251,191,36,.12);border-color:rgba(251,191,36,.35);color:#fde68a}
.game .note-guest a{color:#fbbf24;font-weight:700}
.g-hud{display:flex;align-items:center;gap:12px;flex-wrap:wrap;margin-bottom:14px}
.g-prog{flex:1;min-width:140px;height:10px;background:rgba(255,255,255,.12);border-radius:999px;overflow:hidden}
.g-prog span{display:block;height:100%;background:linear-gradient(90deg,#22d3ee,#a78bfa);border-radius:999px;transition:width .3s}
.g-stat{background:rgba(255,255,255,.08);border-radius:10px;padding:6px 12px;font-weight:700;font-size:.92rem;white-space:nowrap}
.g-stat.combo{color:#fbbf24}
.g-read{border:1px solid transparent;color:#e6eeff;font-family:inherit;cursor:pointer}
.g-read[aria-pressed=false]{opacity:.5;text-decoration:line-through}
.g-read:focus-visible,.g-say:focus-visible{outline:3px solid #38bdf8}
.g-say{float:right;margin:-6px -8px 6px 10px;width:36px;height:36px;border-radius:50%;border:1px solid rgba(255,255,255,.2);background:rgba(255,255,255,.1);color:#fff;font-size:1rem;cursor:pointer}
.g-say:hover{background:rgba(255,255,255,.2)}
@media (max-width:560px){.g-read span{display:none}}
.g-timer{height:6px;background:rgba(255,255,255,.1);border-radius:999px;overflow:hidden;margin-bottom:18px}
.g-timer span{display:block;height:100%;background:linear-gradient(90deg,#34d399,#fbbf24,#f87171);background-size:300% 100%;transform-origin:left}
.g-q{font-size:clamp(1.08rem,2.4vw,1.3rem);font-weight:600;line-height:1.55;color:#fff;background:rgba(255,255,255,.06);border:1px solid rgba(255,255,255,.12);border-radius:18px;padding:20px 22px;margin-bottom:16px}
.g-q sub,.g-q sup,.g-opt sub,.g-opt sup{font-size:.72em}
.q-tag{display:inline-block;font-size:.7rem;font-weight:800;background:rgba(251,191,36,.18);color:#fbbf24;border-radius:999px;padding:2px 8px;margin-right:6px;vertical-align:middle}
.g-opts{display:grid;grid-template-columns:1fr 1fr;gap:12px}
.g-opt{display:flex;align-items:center;gap:12px;text-align:left;background:#fff;color:var(--ink);border:2px solid transparent;border-radius:16px;padding:14px 16px;font:600 1.02rem/1.4 "Be Vietnam Pro",system-ui,sans-serif;cursor:pointer;transition:transform .08s,box-shadow .15s,border-color .15s;min-height:62px}
.g-opt:hover:not([disabled]){transform:translateY(-2px);box-shadow:0 10px 24px -10px rgba(0,0,0,.6);border-color:#93c5fd}
.g-opt .k{width:30px;height:30px;border-radius:9px;background:#e8eefc;color:var(--navy);display:grid;place-items:center;font-weight:800;flex-shrink:0;font-size:.9rem}
.g-opt.right{background:#d1fae5;border-color:#10b981}.g-opt.right .k{background:#10b981;color:#fff}
.g-opt.wrong{background:#fee2e2;border-color:#ef4444}.g-opt.wrong .k{background:#ef4444;color:#fff}
.g-opt[disabled]{cursor:default}
.g-opt.dim{opacity:.55}
.g-opts.tf{grid-template-columns:1fr 1fr}
@media (max-width:640px){.game{padding:18px;border-radius:20px}.g-opts{grid-template-columns:1fr}.g-opts.tf{grid-template-columns:1fr 1fr}}
.g-feedback{margin-top:16px;border-radius:16px;padding:14px 18px;background:rgba(255,255,255,.07);border:1px solid rgba(255,255,255,.14);animation:pop .25s ease}
.g-feedback.ok{border-color:rgba(52,211,153,.5);background:rgba(16,185,129,.12)}
.g-feedback.no{border-color:rgba(248,113,113,.5);background:rgba(239,68,68,.12)}
.g-feedback b{font-size:1.05rem}
.g-feedback .ex{color:#dbe7ff;margin:6px 0 10px;line-height:1.6}
.g-feedback .btn{margin-top:4px}
@keyframes pop{from{transform:scale(.97);opacity:0}to{transform:none;opacity:1}}
.pts-fly{position:absolute;right:30px;top:70px;font-weight:800;font-size:1.4rem;color:#fbbf24;animation:fly 1s ease forwards;pointer-events:none}
@keyframes fly{to{transform:translateY(-40px);opacity:0}}
.race{position:relative;height:92px;background:repeating-linear-gradient(90deg,#334155 0 30px,#3f4d63 30px 60px);border-radius:14px;margin-bottom:16px;overflow:hidden;border:2px solid rgba(255,255,255,.15)}
.race::before{content:"";position:absolute;left:0;right:0;top:50%;border-top:2px dashed rgba(255,255,255,.5)}
.race .finish{position:absolute;right:8px;top:0;bottom:0;width:14px;background:repeating-conic-gradient(#fff 0 25%,#111 0 50%) 0 0/14px 14px}
.car{position:absolute;left:8px;font-size:2rem;transition:left .6s cubic-bezier(.3,1.4,.5,1);transform:scaleX(-1)}
.car.you{top:4px}.car.ai{top:48px}
.car small{position:absolute;transform:scaleX(-1);font-size:.62rem;font-weight:800;top:-4px;left:6px;background:#fbbf24;color:#000;border-radius:6px;padding:0 4px}
.car.ai small{background:#94a3b8}
.g-end{text-align:center;max-width:640px;margin:0 auto}
.g-score{font-size:3.4rem;font-weight:800;color:#fbbf24;line-height:1;margin:6px 0}
.g-end .kpis li{background:rgba(255,255,255,.07);border-color:rgba(255,255,255,.14)}
.g-end .kpis b{color:#fff}.g-end .kpis span{color:#a9bde8}
.new-badges{display:flex;gap:10px;justify-content:center;flex-wrap:wrap;margin:14px 0}
.new-badges div{background:rgba(251,191,36,.15);border:1px solid rgba(251,191,36,.4);border-radius:14px;padding:10px 14px;animation:pop .4s ease}
.g-actions{display:flex;gap:10px;justify-content:center;flex-wrap:wrap;margin-top:16px}
.g-review{margin-top:22px;text-align:left}
.rv-item{background:rgba(255,255,255,.06);border:1px solid rgba(255,255,255,.12);border-radius:14px;padding:14px 16px;margin-bottom:10px}
.rv-item.ok{border-left:4px solid #34d399}.rv-item.no{border-left:4px solid #f87171}
.rv-item ol{margin:8px 0;padding-left:22px}.rv-item li.ans{color:#6ee7b7;font-weight:700}.rv-item li.pick{color:#fca5a5;text-decoration:line-through}
.rv-item .ex{color:#c7d6f7;font-size:.92rem}
.confetti{position:absolute;inset:0;pointer-events:none;overflow:hidden}
.confetti i{position:absolute;top:-12px;width:9px;height:14px;border-radius:2px;animation:fall 2.4s ease-in forwards}
@keyframes fall{to{transform:translateY(560px) rotate(720deg);opacity:.2}}

/* hồ sơ */
.profile{display:flex;gap:20px;align-items:center;padding:24px}
.pf-avatar{width:84px;height:84px;border-radius:24px;background:linear-gradient(135deg,#2563eb,#7c3aed);color:#fff;font-size:2.4rem;font-weight:800;display:grid;place-items:center;flex-shrink:0}
.pf-main{flex:1;min-width:0}.pf-main h1{margin:0}
.lvbar{height:12px;background:#e8eefc;border-radius:999px;overflow:hidden;margin:10px 0 6px}
.lvbar span{display:block;height:100%;background:linear-gradient(90deg,#22d3ee,#2563eb,#7c3aed);border-radius:999px}
.kpis{list-style:none;padding:0;margin:18px 0 0;display:grid;grid-template-columns:repeat(4,1fr);gap:12px}
.kpis li{background:#fff;border:1px solid var(--line);border-radius:14px;padding:14px;text-align:center;display:flex;flex-direction:column}
.kpis b{font-size:1.5rem;color:var(--ink);font-weight:800}.kpis span{font-size:.85rem;color:var(--muted)}
@media (max-width:560px){.kpis{grid-template-columns:1fr 1fr}.profile{flex-direction:column;text-align:center}}
.badges{display:grid;grid-template-columns:repeat(auto-fill,minmax(150px,1fr));gap:10px}
.badge{background:#fff;border:1px solid var(--line);border-radius:14px;padding:14px 10px;text-align:center;display:flex;flex-direction:column;gap:3px;filter:grayscale(1);opacity:.5}
.badge.got{filter:none;opacity:1;border-color:#fcd34d;background:linear-gradient(180deg,#fffbeb,#fff)}
.badge span{font-size:2rem}.badge b{color:var(--ink);font-size:.92rem}.badge small{color:var(--muted);font-size:.75rem;line-height:1.35}

/* biểu mẫu */
.auth{text-align:center;padding:30px 26px;margin:20px auto}
.auth img{margin-bottom:6px}
.form{display:flex;flex-direction:column;gap:14px;text-align:left;margin-top:14px}
.form label{display:flex;flex-direction:column;gap:6px;font-weight:600;font-size:.92rem;color:var(--ink)}
.form input,.form select{font:500 1rem "Be Vietnam Pro",system-ui,sans-serif;padding:12px 14px;border:1.5px solid var(--line);border-radius:12px;background:#fff;color:var(--text)}
.form input:focus,.form select:focus{border-color:var(--blue);outline:none;box-shadow:0 0 0 4px rgba(37,99,235,.12)}
.form details summary{cursor:pointer;font-weight:600;color:var(--blue);margin-bottom:8px}
.form details label{margin-top:10px}

/* lỗi */
.err{text-align:center;padding:50px 0}
.err-code{font-size:6rem;font-weight:800;background:linear-gradient(90deg,#2563eb,#db2777);-webkit-background-clip:text;background-clip:text;color:transparent;line-height:1}

/* chân trang */
.footer{background:#0b1d4a;color:#b9c7e8;margin-top:40px;padding:40px 0 20px}
.footer-in{display:grid;grid-template-columns:1.5fr 1fr 1fr 1fr;gap:28px}
.footer h3{color:#fff;font-size:1rem;margin-bottom:10px}
.footer ul{list-style:none;padding:0;margin:0}.footer li{margin:6px 0}
.footer a{color:#b9c7e8}.footer a:hover{color:#fff}
.f-brand p{font-size:.9rem;margin-top:10px}
.copy{border-top:1px solid rgba(255,255,255,.1);margin-top:26px;padding-top:16px;font-size:.84rem;color:#8b9cc4}
@media (max-width:800px){.footer-in{grid-template-columns:1fr 1fr}.f-brand{grid-column:1/-1}}

@media (max-width:380px){.game-grid,.sim-grid,.lesson-grid,.mm-grid,.tour-grid{grid-template-columns:1fr}}