:root{--bg:#0B0C18;--panel:#16182E;--card:#1C1F3A;--line:#2A2E52;--ink:#EEF0FF;--sub:#A7ABD6;--primary:#7C5CFF;--primary2:#5B8BFF;--accent:#22D3A6;--warn:#FFB020;--pink:#FF6B9D;--grad:linear-gradient(135deg,var(--primary),var(--primary2))}
  :root[data-theme="light"]{--bg:#F5F6FB;--panel:#FFFFFF;--card:#FFFFFF;--line:#E4E7F1;--ink:#191B2E;--sub:#5C6180;--accent:#12A37A}
  :root[data-theme="light"] header{background:rgba(255,255,255,.85)!important}
  :root[data-theme="light"] .blob{opacity:.18}
  :root[data-theme="light"] .search input{background:#EEF0F8}
  :root[data-theme="light"] .content p,:root[data-theme="light"] .content li{color:#2A2D45}
  :root[data-theme="light"] .modtag{color:#191B2E}
  /* keep the phone mockup dark even in light mode */
  :root[data-theme="light"] .p-card{background:#1C1F3A;border-color:#2A2E52}
  :root[data-theme="light"] .p-title,:root[data-theme="light"] .p-card .nm{color:#EEF0FF}
  :root[data-theme="light"] .p-sub,:root[data-theme="light"] .p-cat{color:#A7ABD6}
  .theme-btn{background:var(--card);border:1px solid var(--line);border-radius:11px;width:38px;height:38px;font-size:16px;cursor:pointer;color:var(--ink);flex:none}
  *{margin:0;padding:0;box-sizing:border-box}
  html{scroll-behavior:smooth}
  body{font-family:'Inter',system-ui,sans-serif;background:var(--bg);color:var(--ink);overflow-x:hidden;line-height:1.6;-webkit-font-smoothing:antialiased}
  a{color:inherit;text-decoration:none;cursor:pointer}
  .wrap{max-width:1180px;margin:0 auto;padding:0 22px}
  .grad-text{background:var(--grad);-webkit-background-clip:text;background-clip:text;-webkit-text-fill-color:transparent}
  .blob{position:fixed;border-radius:50%;filter:blur(90px);opacity:.5;z-index:0;pointer-events:none;animation:float 16s ease-in-out infinite}
  .blob.b1{width:420px;height:420px;background:#5b3bff;top:-120px;left:-120px}
  .blob.b2{width:380px;height:380px;background:#1f7fff;top:40%;right:-140px;animation-delay:-6s}
  .blob.b3{width:340px;height:340px;background:#12a37a;bottom:-120px;left:20%;animation-delay:-11s}
  @keyframes float{0%,100%{transform:translate(0,0) scale(1)}50%{transform:translate(30px,-40px) scale(1.12)}}
  header{position:sticky;top:0;z-index:50;backdrop-filter:blur(14px);background:rgba(11,12,24,.72);border-bottom:1px solid transparent;transition:border-color .3s}
  header.scrolled{border-color:var(--line)}
  nav{display:flex;align-items:center;justify-content:space-between;height:66px;gap:16px}
  .logo{display:flex;align-items:center;gap:10px;font-weight:800;font-size:18px}
  .logo .mark{width:38px;height:38px;border-radius:11px;background:var(--grad);display:grid;place-items:center;font-weight:900;font-size:15px;color:#fff;box-shadow:0 6px 18px rgba(124,92,255,.45)}
  .logo .mark::after{content:"</>"}
  .nav-links{display:flex;gap:26px;align-items:center}
  .nav-links a{color:var(--sub);font-size:14px;font-weight:600;transition:color .2s}
  .nav-links a:hover{color:var(--ink)}
  .search{position:relative;width:min(230px,34vw)}
  .search input{width:100%;background:var(--card);border:1px solid var(--line);border-radius:11px;color:var(--ink);padding:9px 13px;font-size:13px;font-family:inherit;outline:none}
  .search input:focus{border-color:var(--primary)}
  .results{position:absolute;top:44px;left:0;right:0;background:var(--panel);border:1px solid var(--line);border-radius:12px;overflow:hidden;max-height:340px;overflow-y:auto;display:none;z-index:60}
  .results.on{display:block}
  .results a{display:block;padding:10px 13px;font-size:13px;border-bottom:1px solid var(--line)}
  .results a:hover{background:var(--card)}
  .results .rc{font-size:10.5px;color:var(--sub)}
  .btn{display:inline-flex;align-items:center;gap:8px;padding:11px 20px;border-radius:12px;font-weight:700;font-size:14px;cursor:pointer;border:none;transition:transform .18s,box-shadow .18s;font-family:inherit}
  .btn-primary{background:var(--grad);color:#fff;box-shadow:0 8px 22px rgba(124,92,255,.4)}
  .btn-primary:hover{transform:translateY(-2px);box-shadow:0 12px 30px rgba(124,92,255,.55)}
  .btn-ghost{background:var(--card);color:var(--ink);border:1px solid var(--line)}
  .btn-ghost:hover{transform:translateY(-2px);border-color:var(--primary)}
  @media(max-width:820px){.nav-links{display:none}.search{width:150px}}
  .hero{position:relative;z-index:1;padding:66px 0 40px;display:grid;grid-template-columns:1.05fr .95fr;gap:30px;align-items:center}
  .pill{display:inline-flex;align-items:center;gap:8px;padding:7px 14px;border-radius:30px;background:var(--card);border:1px solid var(--line);font-size:12.5px;font-weight:600;color:var(--sub);margin-bottom:22px}
  .pill .dot{width:8px;height:8px;border-radius:50%;background:var(--accent);box-shadow:0 0 0 4px rgba(34,211,166,.2)}
  h1{font-size:54px;line-height:1.05;font-weight:900;letter-spacing:-1.5px;margin-bottom:18px}
  .hero p.lead{font-size:17px;color:var(--sub);max-width:480px;margin-bottom:28px}
  .hero-cta{display:flex;gap:14px;flex-wrap:wrap}
  .stats{display:flex;gap:34px;margin-top:36px}
  .stats .n{font-size:26px;font-weight:900}
  .stats .l{font-size:12px;color:var(--sub)}
  @media(max-width:900px){.hero{grid-template-columns:1fr;padding-top:40px}h1{font-size:38px}.phone-wrap{margin:0 auto}}
  .phone-wrap{display:flex;justify-content:center;perspective:1400px}
  .phone{width:290px;height:590px;border-radius:40px;background:#05060f;border:9px solid #191c30;box-shadow:0 40px 80px rgba(0,0,0,.6),0 0 0 1px rgba(124,92,255,.25);padding:16px 14px;position:relative;animation:phoneFloat 6s ease-in-out infinite;transform:rotateY(-14deg) rotateX(4deg)}
  @keyframes phoneFloat{0%,100%{transform:rotateY(-14deg) rotateX(4deg) translateY(0)}50%{transform:rotateY(-10deg) rotateX(3deg) translateY(-16px)}}
  .notch{position:absolute;top:16px;left:50%;transform:translateX(-50%);width:120px;height:22px;background:#191c30;border-radius:0 0 14px 14px}
  .p-head{display:flex;align-items:center;gap:9px;margin:12px 4px 16px}
  .p-logo{width:34px;height:34px;border-radius:10px;background:var(--grad);display:grid;place-items:center;font-size:16px}
  .p-title{font-size:14px;font-weight:800}
  .p-sub{font-size:9.5px;color:var(--sub)}
  .p-streak{margin-left:auto;font-size:10px;font-weight:700;color:var(--warn);background:#2A1E12;border:1px solid #4A381C;padding:5px 8px;border-radius:9px}
  .p-banner{background:var(--grad);border-radius:15px;padding:14px;margin-bottom:14px}
  .p-banner h4{font-size:13px;margin-bottom:5px}
  .p-banner p{font-size:9.5px;color:rgba(255,255,255,.8)}
  .p-cat{font-size:9px;letter-spacing:1px;color:var(--sub);font-weight:800;margin:4px 0 9px}
  .p-grid{display:grid;grid-template-columns:1fr 1fr;gap:9px}
  .p-card{background:var(--card);border:1px solid var(--line);border-radius:13px;padding:11px}
  .p-ic{width:34px;height:34px;border-radius:9px;display:grid;place-items:center;font-size:16px;margin-bottom:20px}
  .p-card .nm{font-size:12px;font-weight:800}
  .p-card .ls{font-size:9px;font-weight:700;margin-top:2px}
  .p-badge{display:inline-block;font-size:7px;font-weight:900;letter-spacing:.4px;color:#fff;background:var(--grad);padding:3px 6px;border-radius:20px;float:right}
  section{position:relative;z-index:1}
  .sec{padding:74px 0}
  .sec-head{text-align:center;max-width:640px;margin:0 auto 46px}
  .sec-head .tag{font-size:12.5px;font-weight:800;letter-spacing:1.5px;color:var(--primary2);text-transform:uppercase}
  .sec-head h2{font-size:38px;font-weight:900;letter-spacing:-1px;margin:12px 0 12px}
  .sec-head p{color:var(--sub);font-size:15.5px}
  .courses{display:grid;grid-template-columns:repeat(4,1fr);gap:16px}
  @media(max-width:900px){.courses{grid-template-columns:repeat(2,1fr)}}
  .course{background:var(--card);border:1px solid var(--line);border-radius:18px;padding:20px;transition:transform .22s,border-color .22s;display:block}
  .course:hover{transform:translateY(-6px);border-color:var(--primary)}
  .course .ctop{display:flex;justify-content:space-between;align-items:flex-start}
  .course .ic{width:52px;height:52px;border-radius:14px;display:grid;place-items:center;font-size:26px;margin-bottom:16px}
  .course h3{font-size:17px;font-weight:800}
  .course .tl{font-size:12px;color:var(--sub);margin:4px 0 12px;min-height:34px}
  .course .ct{font-size:12px;font-weight:700}
  .cbadge{font-size:8px;font-weight:900;letter-spacing:.5px;color:#fff;background:var(--grad);padding:4px 8px;border-radius:20px}
  .feat{background:linear-gradient(135deg,rgba(156,39,176,.18),rgba(91,139,255,.12));border:1px solid var(--line);border-radius:26px;padding:44px;display:grid;grid-template-columns:1.1fr .9fr;gap:34px;align-items:center;overflow:hidden}
  @media(max-width:820px){.feat{grid-template-columns:1fr;padding:30px}}
  .feat .tag2{display:inline-block;font-size:11px;font-weight:900;letter-spacing:1px;background:var(--grad);color:#fff;padding:6px 12px;border-radius:20px;margin-bottom:16px}
  .feat h2{font-size:32px;font-weight:900;letter-spacing:-.5px;margin-bottom:12px}
  .feat p{color:var(--sub);font-size:14.5px;margin-bottom:20px}
  .modtags{display:flex;flex-wrap:wrap;gap:8px}
  .modtag{font-size:11.5px;font-weight:600;color:var(--ink);background:var(--card);border:1px solid var(--line);padding:7px 11px;border-radius:20px}
  .feats{display:grid;grid-template-columns:repeat(3,1fr);gap:18px}
  @media(max-width:820px){.feats{grid-template-columns:1fr}}
  .fcard{background:var(--card);border:1px solid var(--line);border-radius:18px;padding:26px;transition:transform .22s,border-color .22s}
  .fcard:hover{transform:translateY(-6px);border-color:var(--primary)}
  .fcard .fic{width:52px;height:52px;border-radius:14px;background:var(--grad);display:grid;place-items:center;font-size:24px;margin-bottom:16px}
  .fcard h3{font-size:17px;font-weight:800;margin-bottom:8px}
  .fcard p{font-size:13.5px;color:var(--sub)}
  .steps{display:grid;grid-template-columns:repeat(4,1fr);gap:16px}
  @media(max-width:820px){.steps{grid-template-columns:1fr 1fr}}
  .step{text-align:center;padding:10px}
  .step .num{width:52px;height:52px;margin:0 auto 14px;border-radius:50%;background:var(--card);border:1px solid var(--line);display:grid;place-items:center;font-size:20px;font-weight:900;color:var(--primary2)}
  .step h4{font-size:15px;font-weight:800;margin-bottom:6px}
  .step p{font-size:12.5px;color:var(--sub)}
  .cta{background:var(--grad);border-radius:28px;padding:60px 40px;text-align:center}
  .cta h2{font-size:38px;font-weight:900;letter-spacing:-1px;margin-bottom:12px}
  .cta p{font-size:16px;color:rgba(255,255,255,.9);max-width:520px;margin:0 auto 26px}
  .cta .btn-white{background:#fff;color:#1a1140}
  footer{border-top:1px solid var(--line);padding:40px 0;margin-top:60px;position:relative;z-index:1}
  .foot{display:flex;justify-content:space-between;align-items:center;flex-wrap:wrap;gap:16px}
  .foot .sub{color:var(--sub);font-size:13px}
  .reveal{opacity:0;transform:translateY(30px);transition:opacity .7s cubic-bezier(.2,.7,.2,1),transform .7s cubic-bezier(.2,.7,.2,1)}
  .reveal.in{opacity:1;transform:none}
  /* content views */
  #view{position:relative;z-index:1;min-height:70vh}
  .crumb{font-size:13px;color:var(--sub);padding:22px 0 6px}
  .crumb a:hover{color:var(--ink)}
  .chero{border-radius:22px;padding:30px;margin:8px 0 20px;color:#fff;overflow:hidden}
  .chero .ce{font-size:40px}
  .chero h1{font-size:34px;font-weight:900;margin-top:6px;color:#fff}
  .chero p{font-size:14px;color:rgba(255,255,255,.9);margin-top:6px}
  .cbtns{display:flex;gap:12px;margin-bottom:20px;flex-wrap:wrap}
  .cbtn{flex:1;min-width:140px;background:var(--card);border:1px solid var(--line);border-radius:13px;padding:14px;text-align:center;font-weight:800;font-size:14px;transition:border-color .18s,transform .18s}
  .cbtn:hover{border-color:var(--primary);transform:translateY(-2px)}
  .lessonlist{display:grid;gap:11px;padding-bottom:50px}
  .lrow{display:flex;align-items:center;gap:14px;background:var(--card);border:1px solid var(--line);border-radius:14px;padding:15px;transition:border-color .18s,transform .18s}
  .lrow:hover{border-color:var(--primary);transform:translateX(4px)}
  .lnum{width:34px;height:34px;border-radius:10px;display:grid;place-items:center;font-weight:800;font-size:14px;flex:none}
  .lrow .lt{font-size:14.5px;font-weight:700}
  .lrow .arw{margin-left:auto;color:var(--sub);font-size:20px}
  .lesson-wrap{display:grid;grid-template-columns:266px 1fr;gap:28px;padding:20px 0 60px;align-items:start}
  @media(max-width:860px){.lesson-wrap{grid-template-columns:1fr}.side{display:none}.side.open{display:block}}
  .side{position:sticky;top:82px;background:var(--panel);border:1px solid var(--line);border-radius:16px;padding:10px;max-height:calc(100vh - 100px);overflow-y:auto}
  .side .sh{font-size:11px;letter-spacing:1px;font-weight:800;color:var(--sub);padding:8px 10px}
  .side a{display:block;padding:9px 11px;border-radius:9px;font-size:12.8px;color:var(--sub);font-weight:600}
  .side a:hover{background:var(--card);color:var(--ink)}
  .side a.active{background:var(--grad);color:#fff}
  .mobtoggle{display:none}
  @media(max-width:860px){.mobtoggle{display:flex;align-items:center;gap:8px;background:var(--card);border:1px solid var(--line);border-radius:11px;padding:11px 14px;font-weight:700;font-size:13px;margin-bottom:14px;cursor:pointer}}
  .content{min-width:0}
  .ltitle{font-size:28px;font-weight:900;letter-spacing:-.5px;margin-bottom:4px}
  .lmeta{font-size:12.5px;color:var(--sub);margin-bottom:20px}
  .content .lh{font-size:18px;font-weight:800;color:var(--primary2);margin:22px 0 8px}
  .content p{font-size:14.5px;color:#D9DCF5;margin:8px 0}
  .content ul{margin:8px 0 8px 4px;list-style:none}
  .content li{font-size:14.5px;color:#D9DCF5;padding-left:20px;position:relative;margin:5px 0}
  .content li::before{content:"▹";position:absolute;left:0;color:var(--primary);font-weight:800}
  .code{background:#0C0E1A;border:1px solid var(--line);border-radius:11px;color:#8FF0D4;font-family:'JetBrains Mono',monospace;font-size:13px;line-height:1.55;padding:14px 16px;margin:12px 0;overflow-x:auto;white-space:pre}
  .nav-btns{display:flex;gap:12px;margin-top:34px}
  .nav-btns a{flex:1;text-align:center;padding:14px;border-radius:12px;font-weight:800;font-size:13.5px}
  .nb-ghost{background:var(--card);border:1px solid var(--line)}
  .nb-ghost:hover{border-color:var(--primary)}
  .nb-grad{background:var(--grad);color:#fff}
  .nb-dim{opacity:.4;pointer-events:none}
  /* quiz */
  .qcard{background:var(--card);border:1px solid var(--line);border-radius:15px;padding:18px;margin-bottom:14px}
  .qq{font-size:15px;font-weight:800;margin-bottom:12px}
  .opt{border:1px solid var(--line);border-radius:11px;padding:11px 13px;margin-bottom:8px;font-size:13.5px;cursor:pointer;transition:border-color .15s,background .15s}
  .opt:hover{border-color:var(--primary2)}
  .opt.sel{border-color:var(--primary);background:rgba(124,92,255,.12)}
  .opt.correct{border-color:var(--accent);background:rgba(34,211,166,.14)}
  .opt.wrong{border-color:var(--pink);background:rgba(255,107,157,.12)}
  .why{font-size:12.5px;color:var(--sub);margin-top:8px;padding:10px;background:rgba(34,211,166,.08);border-radius:9px}
  .score{text-align:center;font-size:22px;font-weight:900;padding:18px;background:var(--card);border:1px solid var(--line);border-radius:15px;margin:16px 0}
  .taskcard{background:var(--card);border:1px solid var(--line);border-radius:14px;padding:16px;margin-bottom:12px;display:flex;gap:14px}
  .tasknum{width:32px;height:32px;flex:none;border-radius:9px;background:var(--grad);color:#fff;display:grid;place-items:center;font-weight:800}
  .taskcard p{font-size:14px}
  /* AI widget */
  #aibtn{position:fixed;right:20px;bottom:20px;z-index:80;background:var(--grad);color:#fff;border:none;border-radius:30px;padding:13px 18px;font-weight:800;font-size:14px;cursor:pointer;box-shadow:0 10px 26px rgba(124,92,255,.5);font-family:inherit}
  #aipanel{position:fixed;right:20px;bottom:78px;width:min(370px,92vw);height:min(520px,72vh);background:var(--panel);border:1px solid var(--line);border-radius:18px;z-index:80;display:none;flex-direction:column;overflow:hidden;box-shadow:0 20px 60px rgba(0,0,0,.5)}
  #aipanel.on{display:flex}
  .ai-h{padding:14px 16px;background:var(--grad);font-weight:800;display:flex;align-items:center;gap:8px}
  .ai-h .x{margin-left:auto;cursor:pointer;opacity:.9}
  .ai-msgs{flex:1;overflow-y:auto;padding:14px;display:flex;flex-direction:column;gap:10px}
  .ai-b{max-width:85%;padding:10px 13px;border-radius:14px;font-size:13px;line-height:1.5;white-space:pre-wrap}
  .ai-u{align-self:flex-end;background:var(--grad);color:#fff;border-bottom-right-radius:4px}
  .ai-a{align-self:flex-start;background:var(--card);border:1px solid var(--line);border-bottom-left-radius:4px}
  .ai-in{display:flex;gap:8px;padding:12px;border-top:1px solid var(--line)}
  .ai-in input{flex:1;background:var(--card);border:1px solid var(--line);border-radius:11px;color:var(--ink);padding:10px 12px;font-size:13px;font-family:inherit;outline:none}
  .ai-in button{background:var(--grad);color:#fff;border:none;border-radius:11px;padding:0 15px;font-weight:800;cursor:pointer}
  /* code playground */
  .play{display:grid;grid-template-columns:330px 1fr;gap:20px;padding-bottom:50px}
  @media(max-width:880px){.play{grid-template-columns:1fr}}
  .play-tasks .ph{font-size:12px;letter-spacing:1px;font-weight:800;color:var(--sub);margin-bottom:10px}
  .play-editor{background:var(--panel);border:1px solid var(--line);border-radius:14px;overflow:hidden;display:flex;flex-direction:column;position:sticky;top:82px}
  .ed-bar{display:flex;gap:8px;align-items:center;padding:10px 12px;border-bottom:1px solid var(--line)}
  .ed-bar .lang{font-weight:800;font-size:13px}
  .ed-run{margin-left:auto;background:var(--grad);color:#fff;border:none;border-radius:9px;padding:8px 16px;font-weight:800;cursor:pointer;font-family:inherit;font-size:13px}
  .ed-reset{background:var(--card);border:1px solid var(--line);color:var(--ink);border-radius:9px;padding:8px 12px;cursor:pointer;font-family:inherit;font-size:12px}
  #code{width:100%;min-height:230px;background:#0C0E1A;color:#E6FFF5;border:none;outline:none;font-family:'JetBrains Mono',monospace;font-size:13px;line-height:1.55;padding:14px;resize:vertical;white-space:pre;tab-size:2}
  .ed-out{border-top:1px solid var(--line);background:#0C0E1A}
  .pv{width:100%;height:230px;border:none;background:#fff;display:block}
  .conh{font-size:10px;letter-spacing:1px;color:var(--sub);padding:6px 12px;background:var(--card)}
  .cons{margin:0;padding:12px 14px;font-family:'JetBrains Mono',monospace;font-size:12.5px;color:#8FF0D4;white-space:pre-wrap;max-height:240px;overflow:auto}
  .sqlwrap{max-height:260px;overflow:auto;padding:10px}
  .sqltable{width:100%;border-collapse:collapse;font-size:12.5px}
  .sqltable th,.sqltable td{border:1px solid var(--line);padding:6px 10px;text-align:left}
  .sqltable th{background:var(--card)}
  /* auth */
  .auth-btn{display:inline-flex;align-items:center;gap:7px;background:#fff;color:#222;border:none;border-radius:11px;padding:8px 14px;font-weight:800;font-size:13px;cursor:pointer;font-family:inherit}
  .auth-btn .g{color:#4285F4;font-weight:900}
  .auth-user{display:flex;align-items:center;gap:8px}
  .auth-user img{width:30px;height:30px;border-radius:50%;object-fit:cover;background:var(--card)}
  .auth-user .nm{font-size:13px;font-weight:700;max-width:100px;overflow:hidden;text-overflow:ellipsis;white-space:nowrap}
  .auth-user .out{background:var(--card);border:1px solid var(--line);color:var(--ink);border-radius:9px;padding:6px 10px;font-size:11.5px;cursor:pointer;font-family:inherit}
  @media(max-width:560px){.auth-user .nm{display:none}.auth-btn span.t{display:none}}
  .xpchip{display:inline-flex;align-items:center;background:var(--card);border:1px solid var(--line);border-radius:11px;padding:8px 12px;font-size:12px;font-weight:800;color:var(--ink);white-space:nowrap}
  @media(max-width:620px){#xpchip{display:none}}