:root{
    --bg:#0E2138;
    --bg-panel:#152C46;
    --bg-panel-2:#1C3D5F;
    --grid-line: rgba(234,242,248,0.07);
    --grid-line-strong: rgba(234,242,248,0.14);
    --ink:#EAF2F8;
    --ink-dim:#9FB4C8;
    --ink-faint:#6E86A0;
    --teal:#3FBFAD;
    --amber:#F2A93B;
    --green:#7EE787;
    --danger:#F2735B;
    --radius:10px;
    --shadow: 0 10px 30px rgba(0,0,0,0.35);
    --display: 'Space Grotesk', sans-serif;
    --body: 'IBM Plex Sans', sans-serif;
    --mono: 'IBM Plex Mono', monospace;
  }

  *{box-sizing:border-box;}
  html{scroll-behavior:smooth;}
  body{
    margin:0;
    background:var(--bg);
    background-image:
      linear-gradient(var(--grid-line) 1px, transparent 1px),
      linear-gradient(90deg, var(--grid-line) 1px, transparent 1px);
    background-size: 34px 34px;
    color:var(--ink);
    font-family:var(--body);
    line-height:1.55;
    -webkit-font-smoothing:antialiased;
  }

  a{color:inherit;}
  img{max-width:100%;display:block;}
  button{font-family:inherit;}

  ::selection{background:var(--teal); color:#062018;}

  :focus-visible{
    outline:2px solid var(--amber);
    outline-offset:3px;
  }

  .wrap{
    max-width:1180px;
    margin:0 auto;
    padding:0 28px;
  }

  .eyebrow{
    font-family:var(--mono);
    font-size:12.5px;
    letter-spacing:0.14em;
    text-transform:uppercase;
    color:var(--teal);
    display:flex;
    align-items:center;
    gap:10px;
  }
  .eyebrow::before{
    content:"";
    width:22px;height:1px;
    background:var(--teal);
    display:inline-block;
  }

  h1,h2,h3{
    font-family:var(--display);
    margin:0;
    letter-spacing:-0.01em;
  }

  /* ---------- HEADER ---------- */
  header{
    position:sticky;
    top:0;
    z-index:200;
    background:rgba(14,33,56,0.86);
    backdrop-filter:blur(10px);
    border-bottom:1px solid var(--grid-line-strong);
  }
  .nav{
    display:flex;
    align-items:center;
    justify-content:space-between;
    padding:16px 0;
  }
  .brand{
    display:flex;
    align-items:center;
    gap:10px;
    font-family:var(--display);
    font-weight:700;
    font-size:19px;
    text-decoration:none;
  }
  .brand-mark{
    width:34px;height:34px;
    border-radius:8px;
    background:linear-gradient(145deg, var(--teal), var(--amber));
    display:flex;align-items:center;justify-content:center;
    color:#0B1E33;
    font-weight:700;
    font-size:16px;
  }
  .brand small{
    display:block;
    font-family:var(--mono);
    font-weight:400;
    font-size:10.5px;
    color:var(--ink-dim);
    letter-spacing:0.08em;
    text-transform:uppercase;
  }
  nav.links{
    display:flex;
    gap:32px;
    align-items:center;
  }
  nav.links a{
    text-decoration:none;
    color:var(--ink-dim);
    font-size:14.5px;
    font-weight:500;
    transition:color .15s;
  }
  nav.links a:hover{color:var(--ink);}
  nav.links a.current{color:var(--teal);}

  .nav-right{display:flex; align-items:center; gap:14px;}

  .btn{
    font-family:var(--body);
    font-weight:600;
    font-size:14px;
    border-radius:8px;
    padding:10px 18px;
    border:1px solid transparent;
    cursor:pointer;
    transition:transform .12s ease, background .15s, border-color .15s, color .15s;
    display:inline-flex;
    align-items:center;
    gap:8px;
  }
  .btn:active{transform:scale(0.97);}
  .btn-primary{
    background:var(--amber);
    color:#26170B;
  }
  .btn-primary:hover{background:#ffbb52;}
  .btn-ghost{
    background:transparent;
    border-color:var(--grid-line-strong);
    color:var(--ink);
  }
  .btn-ghost:hover{border-color:var(--teal); color:var(--teal);}
  .btn-sm{padding:7px 13px; font-size:13px;}

  .hamburger{
    display:none;
    flex-direction:column;
    gap:5px;
    background:none;border:none;cursor:pointer;
    padding:6px;
  }
  .hamburger span{width:22px;height:2px;background:var(--ink);display:block;}

  /* ---------- HERO ---------- */
  .hero{
    padding:78px 0 60px;
    position:relative;
    overflow:hidden;
  }
  .hero .wrap{
    display:grid;
    grid-template-columns:1.05fr 0.95fr;
    gap:50px;
    align-items:center;
  }
  .hero h1{
    font-size:clamp(34px, 4.6vw, 54px);
    line-height:1.08;
    font-weight:700;
    margin:18px 0 20px;
  }
  .hero h1 .hl-teal{color:var(--teal);}
  .hero h1 .hl-amber{color:var(--amber);}
  .hero p.lead{
    color:var(--ink-dim);
    font-size:16.5px;
    max-width:520px;
    margin:0 0 30px;
  }
  .hero-ctas{display:flex; gap:14px; flex-wrap:wrap;}

  .hero-stats{
    display:flex;
    gap:30px;
    margin-top:42px;
    flex-wrap:wrap;
  }
  .hero-stats div{font-family:var(--mono);}
  .hero-stats b{
    display:block;
    font-size:22px;
    color:var(--ink);
  }
  .hero-stats span{
    font-size:11.5px;
    color:var(--ink-faint);
    text-transform:uppercase;
    letter-spacing:0.06em;
  }

  .blueprint-box{
    background:var(--bg-panel);
    border:1px solid var(--grid-line-strong);
    border-radius:var(--radius);
    padding:18px;
    box-shadow:var(--shadow);
  }
  .blueprint-box .cap{
    display:flex;justify-content:space-between;align-items:center;
    font-family:var(--mono);
    font-size:11px;
    color:var(--ink-faint);
    letter-spacing:0.06em;
    text-transform:uppercase;
    padding-bottom:12px;
    margin-bottom:6px;
    border-bottom:1px dashed var(--grid-line-strong);
  }

  /* draw-in animation for hero svg */
  .draw{
    stroke-dasharray:600;
    stroke-dashoffset:600;
    animation:draw 1.8s ease forwards;
  }
  .draw2{ stroke-dasharray:400; stroke-dashoffset:400; animation:draw 1.8s ease forwards; animation-delay:.3s;}
  .draw3{ stroke-dasharray:400; stroke-dashoffset:400; animation:draw 1.8s ease forwards; animation-delay:.6s;}
  @keyframes draw{ to{ stroke-dashoffset:0; } }
  .fadeInUp{ opacity:0; animation:fadeInUp .7s ease forwards; }
  @keyframes fadeInUp{ from{opacity:0; transform:translateY(10px);} to{opacity:1; transform:translateY(0);} }

  @media (prefers-reduced-motion: reduce){
    .draw,.draw2,.draw3{ animation:none; stroke-dashoffset:0; }
    .fadeInUp{ animation:none; opacity:1; }
    html{scroll-behavior:auto;}
  }

  /* ---------- SECTION SHELL ---------- */
  section{padding:70px 0;}
  .section-head{
    max-width:640px;
    margin-bottom:44px;
  }
  .section-head h2{
    font-size:clamp(26px,3vw,36px);
    margin-top:14px;
  }
  .section-head p{color:var(--ink-dim); font-size:15.5px; margin-top:12px;}

  /* ---------- FEATURES ---------- */
  .features{
    display:grid;
    grid-template-columns:repeat(3,1fr);
    gap:22px;
  }
  .feature-card{
    background:var(--bg-panel);
    border:1px solid var(--grid-line-strong);
    border-radius:var(--radius);
    padding:26px;
    position:relative;
  }
  .feature-card .num{
    font-family:var(--mono);
    font-size:12px;
    color:var(--ink-faint);
  }
  .feature-card h3{
    font-size:18px;
    margin:14px 0 10px;
  }
  .feature-card p{
    color:var(--ink-dim);
    font-size:14.5px;
    margin:0;
  }
  .feature-card .chip{
    display:inline-block;
    margin-top:16px;
    font-family:var(--mono);
    font-size:11px;
    padding:4px 9px;
    border-radius:5px;
    letter-spacing:0.04em;
  }
  .chip-teal{background:rgba(63,191,173,0.14); color:var(--teal);}
  .chip-amber{background:rgba(242,169,59,0.14); color:var(--amber);}
  .chip-green{background:rgba(126,231,135,0.14); color:var(--green);}

  /* ---------- SUBJECTS ---------- */
  .subjects{
    display:grid;
    grid-template-columns:repeat(3,1fr);
    gap:22px;
  }
  .subject-card{
    background:linear-gradient(180deg, var(--bg-panel), var(--bg-panel-2));
    border:1px solid var(--grid-line-strong);
    border-radius:var(--radius);
    padding:26px;
  }
  .subject-card .icon{
    width:44px;height:44px;
    border-radius:8px;
    display:flex;align-items:center;justify-content:center;
    font-family:var(--mono);
    font-weight:600;
    font-size:18px;
    margin-bottom:16px;
  }
  .subject-card h3{font-size:19px; margin-bottom:6px;}
  .subject-card .tagline{
    color:var(--ink-faint);
    font-size:13px;
    font-family:var(--mono);
    margin-bottom:16px;
  }
  .subject-card ul{
    list-style:none; margin:0; padding:0;
    display:flex; flex-direction:column; gap:9px;
  }
  .subject-card li{
    font-size:14px;
    color:var(--ink-dim);
    padding-left:16px;
    position:relative;
  }
  .subject-card li::before{
    content:"—";
    position:absolute;left:0;top:0;
    color:var(--ink-faint);
  }
  .subject-math .icon{background:rgba(63,191,173,0.16); color:var(--teal);}
  .subject-physics .icon{background:rgba(242,169,59,0.16); color:var(--amber);}
  .subject-python .icon{background:rgba(126,231,135,0.16); color:var(--green);}

  /* ---------- NOTES / DOWNLOAD ---------- */
  .notes-panel{
    background:var(--bg-panel);
    border:1px solid var(--grid-line-strong);
    border-radius:var(--radius);
    overflow:hidden;
  }
  .class-tabs{
    display:flex;
    flex-wrap:wrap;
    gap:8px;
    padding:20px 24px;
    border-bottom:1px solid var(--grid-line-strong);
  }
  .tab-btn{
    background:transparent;
    border:1px solid var(--grid-line-strong);
    color:var(--ink-dim);
    padding:9px 16px;
    border-radius:30px;
    font-size:13.5px;
    font-weight:500;
    cursor:pointer;
    transition:all .15s;
  }
  .tab-btn.active{
    background:var(--teal);
    color:#062018;
    border-color:var(--teal);
  }
  .tab-btn:hover:not(.active){border-color:var(--ink-dim); color:var(--ink);}

  .notes-grid{
    padding:26px 24px 30px;
    display:grid;
    grid-template-columns:repeat(3,1fr);
    gap:16px;
  }
  .note-card{
    background:var(--bg-panel-2);
    border:1px solid var(--grid-line-strong);
    border-radius:8px;
    padding:18px;
    display:flex;
    flex-direction:column;
    gap:10px;
  }
  .note-card .subj-tag{
    font-family:var(--mono);
    font-size:10.5px;
    text-transform:uppercase;
    letter-spacing:0.06em;
    width:fit-content;
    padding:3px 8px;
    border-radius:4px;
  }
  .note-card h4{
    font-family:var(--body);
    font-size:15px;
    font-weight:600;
    margin:0;
    color:var(--ink);
  }
  .note-card .meta{
    font-family:var(--mono);
    font-size:11.5px;
    color:var(--ink-faint);
  }
  .note-card .dl-btn{
    margin-top:6px;
    width:100%;
    justify-content:center;
    background:transparent;
    border:1px solid var(--grid-line-strong);
    color:var(--ink);
    font-size:13px;
  }
  .note-card .dl-btn:hover{border-color:var(--amber); color:var(--amber);}
  .note-card .dl-btn.locked::before{content:"🔒 ";}

  .notes-footnote{
    padding:0 24px 24px;
    font-size:12.5px;
    color:var(--ink-faint);
    font-family:var(--mono);
  }

  /* ---------- ABOUT / CTA STRIP ---------- */
  .cta-strip{
    background:var(--bg-panel);
    border:1px solid var(--grid-line-strong);
    border-radius:var(--radius);
    padding:44px;
    display:flex;
    align-items:center;
    justify-content:space-between;
    gap:30px;
    flex-wrap:wrap;
  }
  .cta-strip h3{font-size:24px; max-width:480px;}
  .cta-strip p{color:var(--ink-dim); margin-top:8px; font-size:14.5px;}

  /* ---------- FOOTER ---------- */
  footer{
    border-top:1px solid var(--grid-line-strong);
    padding:44px 0 30px;
    color:var(--ink-faint);
    font-size:13px;
  }
  .footer-grid{
    display:flex;
    justify-content:space-between;
    flex-wrap:wrap;
    gap:24px;
    margin-bottom:24px;
  }
  .footer-grid a{
    display:block;
    color:var(--ink-dim);
    text-decoration:none;
    font-size:13.5px;
    margin-bottom:8px;
  }
  .footer-grid a:hover{color:var(--teal);}
  .footer-col h5{
    font-family:var(--mono);
    font-size:11px;
    text-transform:uppercase;
    letter-spacing:0.08em;
    color:var(--ink-faint);
    margin-bottom:14px;
  }
  .footer-bottom{
    border-top:1px solid var(--grid-line);
    padding-top:20px;
    display:flex;
    justify-content:space-between;
    flex-wrap:wrap;
    gap:10px;
  }

  /* ---------- WHATSAPP FAB ---------- */
  .whatsapp-fab{
    position:fixed;
    right:22px;
    bottom:22px;
    width:56px;height:56px;
    border-radius:50%;
    background:#25D366;
    color:#062018;
    display:flex;
    align-items:center;
    justify-content:center;
    box-shadow:var(--shadow);
    z-index:400;
    transition:transform .15s ease, box-shadow .15s ease;
  }
  .whatsapp-fab:hover{
    transform:translateY(-3px) scale(1.05);
    box-shadow:0 14px 34px rgba(0,0,0,0.45);
  }
  .whatsapp-fab svg{display:block;}

  @media (max-width:600px){
    .whatsapp-fab{
      right:16px;
      bottom:16px;
      width:50px;height:50px;
    }
  }

  /* ---------- RESPONSIVE ---------- */
  @media (max-width:900px){
    .hero .wrap{grid-template-columns:1fr;}
    .features, .subjects{grid-template-columns:1fr 1fr;}
    .notes-grid{grid-template-columns:1fr 1fr;}
    nav.links{display:none;}
    .hamburger{display:flex;}
  }
  @media (max-width:600px){
    .features, .subjects, .notes-grid{grid-template-columns:1fr;}
    .wrap{padding:0 18px;}
    .cta-strip{padding:28px;}
  }
  .video-row {
    display: flex;
    gap: 16px;
    flex-wrap: wrap;
    justify-content: center;
    max-width: 900px;
    margin: 0 auto;
  }
  .video-embed {
    position: relative;
    width: 280px;
    max-width: 100%;
    aspect-ratio: 16 / 9;
    border-radius: 10px;
    overflow: hidden;
  }
  .video-embed iframe {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    border: 0;
  }