/* ===== Reset & tokens ===== */
*{margin:0;padding:0;box-sizing:border-box}
:root{
  --bg:#f7f9fc; --surface:#ffffff; --ink:#0f1b2d; --muted:#5b6b80;
  --line:#e4e9f2; --brand:#0b5bd3; --brand2:#06b6c4; --accent:#ff7a18;
  --good:#0f9d58; --bad:#e0392b; --warn:#c97a00;
  --grad:linear-gradient(120deg,#0b5bd3,#06b6c4);
  --shadow:0 10px 40px -12px rgba(15,27,45,.18);
  --r:16px; --sb:280px;
  font-family:system-ui,"Segoe UI",Roboto,"Helvetica Neue",Arial,"Apple Color Emoji",sans-serif;
}
html{scroll-behavior:smooth;scroll-padding-top:24px}
body{background:var(--bg);color:var(--ink);line-height:1.65;-webkit-font-smoothing:antialiased}
a{color:var(--brand);text-decoration:none}
em{font-style:normal;color:var(--brand);font-weight:600}
code{font-family:"SF Mono",Menlo,Consolas,monospace;background:#eef2f9;padding:2px 6px;border-radius:6px;font-size:.9em}

/* ===== Progress bar ===== */
#scrollProgress{position:fixed;top:0;left:0;height:3px;width:0;background:var(--grad);z-index:100;transition:width .1s}

/* ===== Sidebar ===== */
#sidebar{position:fixed;top:0;left:0;width:var(--sb);height:100vh;background:var(--surface);
  border-right:1px solid var(--line);padding:24px 18px;display:flex;flex-direction:column;z-index:60;overflow-y:auto}
.brand{display:flex;gap:12px;align-items:center;margin-bottom:24px}
.brand .logo{width:42px;height:42px;border-radius:12px;background:var(--grad);color:#fff;font-weight:800;
  display:grid;place-items:center;font-size:18px;letter-spacing:.5px}
.brand strong{display:block;font-size:15px}
.brand small{color:var(--muted);font-size:12px}
#toc{display:flex;flex-direction:column;gap:2px;flex:1}
#toc a{display:flex;align-items:center;gap:10px;padding:9px 12px;border-radius:10px;color:var(--muted);
  font-size:14px;font-weight:500;transition:.15s}
#toc a .num{width:22px;height:22px;border-radius:7px;background:#eef2f9;color:var(--muted);
  display:grid;place-items:center;font-size:12px;font-weight:700;flex:none}
#toc a:hover{background:#f1f5fb;color:var(--ink)}
#toc a.active{background:#eaf1fe;color:var(--brand)}
#toc a.active .num{background:var(--brand);color:#fff}
.sidebar-foot{display:flex;align-items:center;gap:12px;margin-top:18px;padding-top:16px;border-top:1px solid var(--line)}
.prog-ring{width:48px;height:48px;border-radius:50%;display:grid;place-items:center;font-size:12px;font-weight:700;color:var(--brand);
  background:conic-gradient(var(--brand) var(--p,0%),#eef2f9 0)}
.prog-ring span{background:var(--surface);width:36px;height:36px;border-radius:50%;display:grid;place-items:center}
.sidebar-foot small{color:var(--muted);font-size:12px}

#menuToggle{display:none;position:fixed;top:14px;left:14px;z-index:70;width:42px;height:42px;border:none;
  border-radius:10px;background:var(--surface);box-shadow:var(--shadow);font-size:20px;cursor:pointer}

/* ===== Layout ===== */
main{margin-left:var(--sb)}
.block{max-width:980px;margin:0 auto;padding:72px 40px}
.block.alt{background:var(--surface);max-width:none}
.block.alt > *{max-width:980px;margin-left:auto;margin-right:auto}
.block-head{margin-bottom:28px}
.step{display:inline-block;font-size:12px;font-weight:700;letter-spacing:.6px;text-transform:uppercase;
  color:var(--brand);background:#eaf1fe;padding:5px 12px;border-radius:30px;margin-bottom:14px}
h2{font-size:clamp(26px,3.4vw,38px);line-height:1.2;letter-spacing:-.5px}
h3{font-size:18px;margin-bottom:8px}
.big{font-size:19px;color:#26384f;margin-bottom:28px;max-width:760px}
.muted{color:var(--muted)} .small{font-size:13px}
.mini-h{margin:34px 0 16px;font-size:20px}

/* ===== Hero ===== */
.hero{background:radial-gradient(1200px 600px at 80% -10%,#0b5bd3 0,#072a63 45%,#04132f 100%);
  color:#eaf2ff;padding:96px 40px;display:grid;grid-template-columns:1.1fr .9fr;gap:48px;align-items:center;min-height:90vh}
.hero-inner{max-width:620px;justify-self:end}
.kicker{display:inline-block;font-size:13px;font-weight:600;color:#9fc2ff;border:1px solid rgba(159,194,255,.35);
  padding:6px 14px;border-radius:30px;margin-bottom:22px}
.hero h1{font-size:clamp(34px,5vw,58px);line-height:1.05;letter-spacing:-1px;margin-bottom:20px}
.grad{background:linear-gradient(90deg,#5ad1ff,#7affd6);-webkit-background-clip:text;background-clip:text;color:transparent}
.lead{font-size:19px;color:#c7d8f5;margin-bottom:32px;max-width:520px}
.hero-cta{display:flex;gap:14px;flex-wrap:wrap}
.btn{display:inline-flex;align-items:center;gap:8px;padding:13px 24px;border-radius:12px;font-weight:600;
  font-size:15px;cursor:pointer;border:none;transition:.18s;font-family:inherit}
.btn.primary{background:#fff;color:#0b3a86}
.btn.primary:hover{transform:translateY(-2px);box-shadow:0 12px 30px -8px rgba(255,255,255,.4)}
.btn.ghost{background:rgba(255,255,255,.08);color:#fff;border:1px solid rgba(255,255,255,.25)}
.btn.ghost:hover{background:rgba(255,255,255,.16)}
.btn.small{padding:9px 16px;font-size:13px;background:var(--brand);color:#fff}
.btn.small.primary{background:var(--brand)}
.hero-stats{display:flex;gap:32px;margin-top:40px;flex-wrap:wrap}
.hero-stats strong{display:block;font-size:22px;color:#fff}
.hero-stats small{color:#9fb6dc;font-size:13px}

.hero-chat{justify-self:start;width:100%;max-width:420px}
.chat-window{background:rgba(255,255,255,.07);border:1px solid rgba(255,255,255,.15);border-radius:18px;
  padding:18px;backdrop-filter:blur(6px);box-shadow:0 30px 60px -20px rgba(0,0,0,.5)}
.cw-bar{display:flex;gap:7px;margin-bottom:16px}
.cw-bar span{width:11px;height:11px;border-radius:50%;background:rgba(255,255,255,.3)}
.bubble{padding:12px 16px;border-radius:14px;margin-bottom:12px;font-size:14.5px;max-width:88%}
.bubble.user{background:#2b6fe0;color:#fff;margin-left:auto;border-bottom-right-radius:4px}
.bubble.ai{background:rgba(255,255,255,.92);color:#16263d;border-bottom-left-radius:4px;min-height:24px}
.bubble.ai::after{content:"▍";color:var(--brand);animation:blink 1s infinite}
.bubble.ai.done::after{content:""}
@keyframes blink{50%{opacity:0}}

/* ===== Cards ===== */
.cards-3{display:grid;grid-template-columns:repeat(3,1fr);gap:18px;margin:24px 0}
.card{background:var(--surface);border:1px solid var(--line);border-radius:var(--r);padding:24px;transition:.2s}
.block.alt .card{background:var(--bg)}
.card:hover{transform:translateY(-4px);box-shadow:var(--shadow);border-color:#cfe0fb}
.card .ic{font-size:30px;margin-bottom:12px}
.card p{color:var(--muted);font-size:14.5px}

/* ===== Callouts ===== */
.callout{background:#eaf1fe;border-left:4px solid var(--brand);padding:18px 22px;border-radius:12px;margin:24px 0;font-size:15px}
.callout.tip{background:#e7f8f0;border-color:var(--good)}
.callout.warn{background:#fff4e2;border-color:var(--warn)}
.block-code{display:block;background:#0f1b2d;color:#9fffd6;padding:14px 16px;border-radius:10px;margin-top:10px;
  font-size:13.5px;line-height:1.6;white-space:pre-wrap}

/* ===== FAQ / details ===== */
.faq{margin-top:24px;background:var(--surface);border:1px solid var(--line);border-radius:12px;padding:4px 20px}
.block.alt .faq{background:var(--bg)}
.faq summary{cursor:pointer;font-weight:600;padding:14px 0;list-style:none}
.faq summary::-webkit-details-marker{display:none}
.faq summary::before{content:"＋";color:var(--brand);font-weight:700;margin-right:10px}
.faq[open] summary::before{content:"－"}
.glossary{list-style:none;padding-bottom:14px;display:grid;gap:8px}
.glossary li{font-size:14.5px;color:var(--muted)}
.glossary b{color:var(--ink)}

/* ===== Model market ===== */
.filter-bar{display:flex;gap:10px;flex-wrap:wrap;margin-bottom:24px}
.chip{padding:8px 16px;border-radius:30px;border:1px solid var(--line);background:var(--surface);
  font-size:13.5px;font-weight:500;cursor:pointer;transition:.15s;color:var(--muted);font-family:inherit}
.chip:hover{border-color:var(--brand);color:var(--brand)}
.chip.active{background:var(--brand);color:#fff;border-color:var(--brand)}
.model-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(260px,1fr));gap:16px}
.model{background:var(--surface);border:1px solid var(--line);border-radius:var(--r);padding:22px;transition:.2s;position:relative}
.block.alt .model{background:var(--bg)}
.model:hover{box-shadow:var(--shadow);transform:translateY(-3px)}
.model-top{display:flex;align-items:center;gap:12px;margin-bottom:12px}
.model-logo{width:44px;height:44px;border-radius:11px;display:grid;place-items:center;font-size:20px;font-weight:800;color:#fff}
.model h3{margin:0;font-size:17px}
.model .maker{font-size:12.5px;color:var(--muted)}
.model p{font-size:14px;color:var(--muted);margin-bottom:12px}
.model .best{font-size:12.5px;font-weight:600;color:var(--brand);background:#eaf1fe;padding:4px 10px;border-radius:8px;display:inline-block}
.model .pill{position:absolute;top:18px;right:18px;font-size:11px;font-weight:700;padding:3px 9px;border-radius:20px}
.pill.free{background:#e7f8f0;color:var(--good)} .pill.paid{background:#fdeceb;color:var(--bad)}

/* ===== Ladder ===== */
.ladder{display:grid;gap:14px}
.rung{background:var(--surface);border:1px solid var(--line);border-radius:var(--r);padding:22px 24px;
  border-left:4px solid var(--brand);transition:.2s}
.rung:hover{box-shadow:var(--shadow)}
.rung .lvl{font-size:12px;font-weight:700;color:var(--brand);text-transform:uppercase;letter-spacing:.5px}
.rung h3{margin:6px 0}
.rung p{color:var(--muted);font-size:15px}
.rung .tag{display:inline-block;margin-top:10px;font-size:12.5px;color:var(--muted);background:#f1f5fb;padding:4px 12px;border-radius:8px}

/* ===== Prompt formula ===== */
.formula{display:flex;align-items:stretch;gap:10px;flex-wrap:wrap;margin:24px 0}
.f-part{flex:1;min-width:160px;background:var(--surface);border:1px solid var(--line);border-radius:14px;padding:16px 18px}
.f-part span{font-size:13px;font-weight:700;color:var(--brand)}
.f-part p{font-size:14px;color:var(--muted);margin-top:6px}
.plus{display:grid;place-items:center;font-size:24px;color:var(--brand);font-weight:700}

/* ===== Compare prompt ===== */
.compare{display:grid;gap:14px}
.cmp-card{background:var(--surface);border:1px solid var(--line);border-radius:var(--r);overflow:hidden}
.cmp-head{padding:14px 20px;font-weight:600;cursor:pointer;display:flex;justify-content:space-between;align-items:center}
.cmp-head .q{color:var(--muted);font-weight:500;font-size:14px}
.cmp-body{display:none;padding:0 20px 20px;grid-template-columns:1fr 1fr;gap:16px}
.cmp-card.open .cmp-body{display:grid}
.cmp-col{border-radius:12px;padding:16px;font-size:14px}
.cmp-col.bad{background:#fdeceb}.cmp-col.good{background:#e7f8f0}
.cmp-col h4{font-size:13px;text-transform:uppercase;letter-spacing:.5px;margin-bottom:8px}
.cmp-col.bad h4{color:var(--bad)}.cmp-col.good h4{color:var(--good)}
.cmp-col .pr{font-family:inherit;background:rgba(255,255,255,.6);padding:10px;border-radius:8px;margin-bottom:8px;font-style:italic}
.cmp-col .res{font-size:13px;color:#3a4d63}

/* ===== Tips grid ===== */
.tips-grid{display:grid;grid-template-columns:repeat(2,1fr);gap:14px;margin-top:24px}
.tip-item{background:var(--surface);border:1px solid var(--line);border-radius:12px;padding:16px 18px;font-size:14.5px;color:var(--muted)}
.tip-item b{color:var(--ink)}

/* ===== Steps ===== */
.steps{display:grid;grid-template-columns:repeat(4,1fr);gap:14px;margin:24px 0}
.stp{background:var(--surface);border:1px solid var(--line);border-radius:14px;padding:20px}
.stp span{width:34px;height:34px;border-radius:10px;background:var(--grad);color:#fff;display:grid;place-items:center;font-weight:700;margin-bottom:10px}
.stp p{font-size:14px;color:var(--muted)}

/* ===== Flow ===== */
.flow{display:flex;align-items:center;justify-content:center;gap:8px;flex-wrap:wrap;margin:28px 0}
.node{background:var(--surface);border:1px solid var(--line);border-radius:16px;padding:20px 24px;text-align:center;font-size:28px;min-width:150px}
.node span{display:block;font-size:15px;font-weight:700;color:var(--ink);margin-top:6px}
.node small{display:block;font-size:12.5px;color:var(--muted);margin-top:2px}
.node.ai{border-color:var(--brand);box-shadow:0 0 0 3px #eaf1fe}
.arrow{font-size:24px;color:var(--brand)}

/* ===== Use cases ===== */
.uc-grid{display:grid;grid-template-columns:repeat(auto-fill,minmax(280px,1fr));gap:16px}
.uc{background:var(--surface);border:1px solid var(--line);border-radius:var(--r);padding:22px;transition:.2s}
.uc:hover{box-shadow:var(--shadow);transform:translateY(-3px)}
.uc .ic{font-size:26px}
.uc h3{margin:10px 0 6px;font-size:16px}
.uc p{font-size:14px;color:var(--muted);margin-bottom:14px}
.uc .pr-mini{background:#0f1b2d;color:#9fffd6;font-size:12.5px;padding:10px 12px;border-radius:10px;
  position:relative;cursor:pointer;line-height:1.5}
.uc .pr-mini:hover{outline:2px solid var(--brand2)}
.uc .pr-mini .copy{position:absolute;top:8px;right:8px;font-size:11px;color:#9fb6dc;background:rgba(255,255,255,.1);
  padding:2px 8px;border-radius:6px}

/* ===== Playground ===== */
.play-grid{display:grid;grid-template-columns:1fr 1fr;gap:20px;margin-bottom:20px}
.panel{background:var(--surface);border:1px solid var(--line);border-radius:var(--r);padding:24px}
.block.alt .panel{background:var(--bg)}
.panel h3{font-size:18px;margin-bottom:6px}
.panel label{display:block;font-size:13.5px;font-weight:600;color:var(--ink);margin-top:14px}
.panel input{width:100%;margin-top:6px;padding:11px 14px;border:1px solid var(--line);border-radius:10px;
  font-family:inherit;font-size:14px;background:var(--surface)}
.panel input:focus{outline:none;border-color:var(--brand);box-shadow:0 0 0 3px #eaf1fe}
.badge{font-size:11px;font-weight:700;background:#fff4e2;color:var(--warn);padding:3px 8px;border-radius:20px;vertical-align:middle}
.prompt-out{margin-top:18px}
.prompt-out pre{background:#0f1b2d;color:#cfe9ff;padding:16px;border-radius:12px;white-space:pre-wrap;
  font-family:inherit;font-size:13.5px;line-height:1.6;min-height:80px}
.prompt-out .btn{margin-top:10px}

/* Simulated chat */
.sim-suggest{display:flex;gap:8px;flex-wrap:wrap;margin:12px 0}
.sim-suggest button{font-size:12.5px;border:1px solid var(--line);background:var(--surface);border-radius:20px;
  padding:7px 14px;cursor:pointer;color:var(--brand);font-family:inherit}
.sim-suggest button:hover{background:#eaf1fe}
.sim-chat{min-height:140px;max-height:320px;overflow-y:auto;display:flex;flex-direction:column;gap:10px;
  padding:14px;background:var(--bg);border-radius:12px;margin-bottom:12px}
.block.alt .sim-chat{background:var(--surface)}
.sim-chat:empty::before{content:"Chọn một gợi ý phía trên hoặc gõ thử…";color:var(--muted);font-size:14px}
.sm{padding:10px 14px;border-radius:12px;font-size:14px;max-width:85%}
.sm.u{background:var(--brand);color:#fff;align-self:flex-end;border-bottom-right-radius:4px}
.sm.a{background:var(--surface);border:1px solid var(--line);align-self:flex-start;border-bottom-left-radius:4px}
.block.alt .sm.a{background:var(--bg)}
.sim-input{display:flex;gap:8px}
.sim-input input{flex:1;padding:11px 14px;border:1px solid var(--line);border-radius:10px;font-family:inherit;font-size:14px}
.faq.live{margin-top:16px}
.faq.live input{width:100%;margin:8px 0;padding:10px 12px;border:1px solid var(--line);border-radius:10px;font-family:inherit}

/* Quiz */
.quiz{margin-top:4px}
.q-item{padding:18px 0;border-bottom:1px solid var(--line)}
.q-item:last-child{border:none}
.q-item .qq{font-weight:600;margin-bottom:12px}
.q-opts{display:grid;gap:8px}
.q-opts button{text-align:left;padding:12px 16px;border:1px solid var(--line);background:var(--surface);
  border-radius:10px;cursor:pointer;font-family:inherit;font-size:14.5px;transition:.15s}
.block.alt .q-opts button{background:var(--bg)}
.q-opts button:hover{border-color:var(--brand)}
.q-opts button.correct{background:#e7f8f0;border-color:var(--good);color:#0a6e3f}
.q-opts button.wrong{background:#fdeceb;border-color:var(--bad);color:#a02218}
.q-opts button.disabled{pointer-events:none;opacity:.65}
.q-fb{margin-top:10px;font-size:14px;color:var(--muted);display:none}
.q-fb.show{display:block}
.quiz-result{margin-top:18px;padding:18px;border-radius:12px;background:#eaf1fe;font-size:16px;font-weight:600;text-align:center}

/* Safety */
.safety-grid{display:grid;grid-template-columns:1fr 1fr;gap:18px;margin-bottom:20px}
.s-card{border-radius:var(--r);padding:24px}
.s-card.bad{background:#fdeceb;border:1px solid #f6c6c1}
.s-card.good{background:#e7f8f0;border:1px solid #b9e6cd}
.s-card h3{margin-bottom:12px}
.s-card ul{padding-left:20px;display:grid;gap:8px}
.s-card li{font-size:14.5px}

/* Footer */
footer{background:#0f1b2d;color:#aebfd6;padding:40px;text-align:center}
footer strong{color:#fff}
footer .small{margin-top:8px;color:#7d92b4}

#toTop{position:fixed;bottom:24px;right:24px;width:46px;height:46px;border-radius:50%;border:none;
  background:var(--brand);color:#fff;font-size:20px;cursor:pointer;box-shadow:var(--shadow);z-index:50}

/* ===== Responsive ===== */
@media(max-width:1024px){
  .hero{grid-template-columns:1fr;text-align:center}
  .hero-inner{justify-self:center} .hero-cta,.hero-stats{justify-content:center}
  .hero-chat{justify-self:center;margin-top:20px}
  .cards-3{grid-template-columns:1fr 1fr}
  .steps{grid-template-columns:1fr 1fr}
}
@media(max-width:820px){
  :root{--sb:0px}
  #sidebar{transform:translateX(-100%);transition:.25s;width:280px;box-shadow:var(--shadow)}
  #sidebar.open{transform:translateX(0)}
  #menuToggle{display:block}
  main,.hero,footer{margin-left:0}
  .hero{padding:90px 24px 60px}
  .block{padding:56px 22px}
  .cards-3,.tips-grid,.play-grid,.safety-grid,.formula,.steps{grid-template-columns:1fr}
  .cmp-body{grid-template-columns:1fr!important}
  .flow{flex-direction:column}.arrow{transform:rotate(90deg)}
}