*{box-sizing:border-box}html{scroll-behavior:smooth}body{margin:0;font-family:Inter,Segoe UI,Arial,sans-serif;color:#0b2857;background:#f7faff}a{color:inherit}.topbar{height:64px;padding:0 max(22px,4.5vw);display:flex;align-items:center;gap:34px;background:#fff;border-bottom:1px solid #e2e9f2;position:sticky;top:0;z-index:30}.brand{display:flex;gap:10px;align-items:center;text-decoration:none;margin-right:auto}.brain{font-size:30px}.brand strong{display:block;font-size:21px;line-height:1}.brand small{display:block;font-size:11px;margin-top:3px}.topbar nav{height:100%;display:flex;gap:30px;align-items:center}.topbar nav a{text-decoration:none;font-size:14px;height:100%;display:flex;align-items:center;border-bottom:2px solid transparent}.topbar nav a.active{color:#087df1;border-bottom-color:#087df1}.market{display:flex;gap:8px;align-items:center;color:#526581;font-size:14px}.globe{font-size:22px}.market select{border:1px solid #cad6e5;border-radius:8px;padding:9px 30px 9px 10px;background:#fff;color:#102a55;font-weight:700}.hero{min-height:318px;display:grid;grid-template-columns:48% 52%;overflow:hidden;background:#fff}.hero-copy{padding:24px 10px 22px max(22px,4.5vw);z-index:2;background:linear-gradient(90deg,#fff 78%,rgba(255,255,255,.75) 93%,rgba(255,255,255,0))}.hero h1{font-size:clamp(38px,3.7vw,58px);line-height:1.03;margin:0 0 12px;letter-spacing:-1.8px}.hero p{font-size:clamp(17px,1.35vw,21px);line-height:1.35;color:#536783;max-width:700px;margin:0}.hero-art{background:linear-gradient(90deg,rgba(255,255,255,.20),rgba(255,255,255,0) 25%),url("../images/hero.webp") center/cover no-repeat}.features{display:flex;gap:clamp(18px,3vw,54px);margin-top:24px;align-items:flex-start}.features span{text-align:center;min-width:84px}.features i{font-style:normal;font-size:29px;display:block}.features b{display:block;font-size:12.5px;line-height:1.35;margin-top:5px;font-weight:500}.notices{display:grid;grid-template-columns:1fr 1fr;gap:12px;padding:10px max(22px,4.5vw)}.notice{padding:13px 18px;border-radius:8px;font-size:13px}.release{background:#fff3f3;border:1px solid #ffd0d0;color:#a51d1d}.revision{background:#f0fbf3;border:1px solid #d5f1dc;color:#234b35}.books{padding:0 max(22px,4.5vw) 30px}.tabs{display:grid;grid-template-columns:repeat(3,1fr);border:1px solid #dce5f0;border-radius:9px 9px 0 0;overflow:hidden}.tab{border:0;border-right:1px solid #dce5f0;background:#f8fbff;color:#102a55;padding:12px 8px;cursor:pointer;min-height:67px}.tab:last-child{border-right:0}.tab b{display:block;font-size:18px}.tab small{display:block;margin-top:5px;font-size:13px}.tab.active{background:#087df1;color:#fff}.reader-shell{position:relative;height:min(51vw,560px);min-height:390px;background:#edf1f5;border:1px solid #dce5f0;border-top:0;border-radius:0 0 10px 10px;overflow:hidden}.reader-host,.reader-host iframe{width:100%;height:100%;border:0;display:block}.loading{position:absolute;inset:0;z-index:5;display:flex;flex-direction:column;justify-content:center;align-items:center;text-align:center;background:linear-gradient(#f8fafc,#e9edf1);transition:opacity .3s ease}.loading.done{opacity:0;pointer-events:none}.loading strong{font-size:17px;margin:13px 0}.loading small{color:#5f728d;margin-top:11px}.spinner{width:44px;height:44px;border:6px solid #d7e1ed;border-top-color:#087df1;border-radius:50%;animation:spin .8s linear infinite}@keyframes spin{to{transform:rotate(360deg)}}.progress{height:8px;width:min(390px,70%);background:#d9e3ef;border-radius:99px;overflow:hidden}.progress span{display:block;width:7%;height:100%;background:#087df1;border-radius:99px;transition:width .25s ease}.buybar{margin-top:12px;background:#fff;border:1px solid #dce5f0;border-radius:10px;display:grid;grid-template-columns:190px 1fr 1.35fr 240px;gap:18px;padding:15px 18px;align-items:center}.buy-section,.resource-link{border-left:1px solid #dce5f0;padding-left:18px}.buy-title b{font-size:19px}.buy-title small{display:block;color:#667892;margin-top:4px}.buybar strong{font-size:13px}.store-links{display:flex;gap:8px;flex-wrap:wrap;margin-top:7px}.store{display:inline-flex;align-items:center;gap:7px;text-decoration:none;border:1px solid #d7e1ed;border-radius:7px;padding:9px 11px;background:#fff;color:#056bd8;font-size:13px}.store:hover{border-color:#087df1;background:#f5faff}.resource-link{text-decoration:none;color:#056bd8;font-weight:700;font-size:13px}footer{display:flex;justify-content:space-between;gap:20px;padding:24px max(22px,4.5vw);background:#102a55;color:#fff;font-size:13px}footer a{color:#fff}@media(max-width:900px){.topbar nav{display:none}.topbar{padding:0 15px}.market label,.globe{display:none}.hero{grid-template-columns:1fr}.hero-art{height:180px;grid-row:1;background-position:center}.hero-copy{padding:25px 18px;background:#fff}.hero h1{font-size:41px}.features{display:grid;grid-template-columns:repeat(3,1fr);gap:17px}.notices{grid-template-columns:1fr;padding:10px 14px}.books{padding:0 14px 25px}.tab{min-height:54px;padding:11px 4px}.tab b{font-size:15px}.tab small{display:none}.reader-shell{height:65vh;min-height:420px}.buybar{grid-template-columns:1fr;gap:12px}.buy-section,.resource-link{border-left:0;border-top:1px solid #dce5f0;padding:12px 0 0}.resource-link{display:block}.brand strong{font-size:16px}}@media(max-width:520px){.hero h1{font-size:35px}.hero p{font-size:17px}.features{grid-template-columns:repeat(2,1fr)}.reader-shell{height:60vh;min-height:380px}.market select{max-width:145px}}
/* v4 compact hero/header treatment */
.brand strong{font-size:22px}
.hero{min-height:230px;grid-template-columns:46% 54%}
.hero-copy{padding-top:18px;padding-bottom:12px}
.hero h1{font-size:clamp(31px,3vw,46px);line-height:1.02;margin-bottom:8px;letter-spacing:-1.25px}
.hero p{font-size:clamp(15px,1.12vw,18px);line-height:1.28;max-width:650px}
.features{margin-top:16px;gap:clamp(15px,2.7vw,46px)}
.features i{font-size:25px}
.features b{font-size:11.5px;margin-top:3px}
.notices{padding-top:7px;padding-bottom:7px}
.notice{padding:10px 16px}
.tab.coming-soon{cursor:not-allowed;background:#f4f6f9;color:#8795aa;opacity:1}
.tab.coming-soon b,.tab.coming-soon small{color:#8795aa}
.tab.coming-soon em{font-style:normal;color:#e31b23;font-size:12px;margin-left:4px}
@media(max-width:900px){
  .hero{min-height:auto}
  .hero h1{font-size:34px}
  .hero-art{height:145px}
  .hero-copy{padding-top:18px;padding-bottom:14px}
}

/* v5: purchase market selector belongs with the retailer choices */
.buybar{grid-template-columns:225px 1fr 1.35fr 240px}
.buy-market{display:flex;align-items:center;gap:7px;margin-top:8px}
.buy-market label{font-size:12px;color:#667892;white-space:nowrap}
.buy-market select{min-width:105px;max-width:145px;border:1px solid #cad6e5;border-radius:7px;padding:7px 25px 7px 8px;background:#fff;color:#102a55;font-weight:700;font-size:12px}
@media(max-width:900px){
  .buybar{grid-template-columns:1fr}
  .buy-market select{max-width:none}
}

/* v6: GitHub/Colab promoted in hero features; removed from purchase bar */
.feature-link{color:#0b2857;text-decoration:none;text-align:center;min-width:84px}
.feature-link b{display:block;font-size:11.5px;line-height:1.35;margin-top:3px;font-weight:500}
.github-feature{transition:color .15s ease,transform .15s ease}
.github-feature:hover,.github-feature:focus-visible{color:#087df1;transform:translateY(-1px)}
.github-icon{display:block;width:27px;height:27px;margin:0 auto}
.buybar{grid-template-columns:225px 1fr 1.35fr}
@media(max-width:900px){
  .buybar{grid-template-columns:1fr}
  .feature-link{min-width:0}
}

/* v7: make GitHub code + Colab resource prominent */
.github-feature{
  min-width:150px;
  padding:5px 9px 6px;
  border:1px solid #cfe0f5;
  border-radius:9px;
  background:#f5faff;
}
.github-feature .github-icon{
  width:30px;
  height:30px;
}
.github-feature b{
  font-size:12.5px;
  line-height:1.3;
  font-weight:700;
  color:#0b2857;
}
.github-feature .github-code{
  color:#087df1;
}
.github-feature:hover,.github-feature:focus-visible{
  background:#eaf5ff;
  border-color:#87bdf5;
  box-shadow:0 3px 10px rgba(8,125,241,.10);
}
@media(max-width:900px){
  .github-feature{min-width:0}
}

/* v8: four focused hero benefits, evenly distributed */
.features{
  display:grid;
  grid-template-columns:repeat(4,minmax(0,1fr));
  gap:12px;
  width:100%;
  max-width:650px;
  align-items:center;
}
.features span,.feature-link{
  min-width:0;
  width:100%;
  justify-self:stretch;
}
.github-feature{
  min-width:0;
  padding:5px 5px 6px;
}
.github-feature .github-icon{
  width:27px;
  height:27px;
}
.github-feature b{
  font-size:11.5px;
}
@media(max-width:900px){
  .features{
    grid-template-columns:repeat(2,minmax(0,1fr));
    max-width:none;
  }
}

/* v11: worldwide market selector + softer ownership invitation */
.buy-title b{font-size:17px;line-height:1.2}
.buy-market select{min-width:150px;max-width:185px}
.buybar{grid-template-columns:255px 1fr 1.35fr}
@media(max-width:900px){
  .buybar{grid-template-columns:1fr}
  .buy-market select{max-width:220px}
}

/* v12: Python + PyTorch marks for the "from Zero" feature */
.python-pytorch-feature{display:block;text-align:center;min-width:0}
.tech-logos{
  height:29px;
  display:flex !important;
  align-items:center;
  justify-content:center;
  gap:8px;
  margin:0 auto;
}
.tech-logos svg{display:block;width:29px;height:29px}
.tech-logos .python-mark{width:31px;height:31px}
.tech-logos .pytorch-mark{width:28px;height:28px}
.python-pytorch-feature b{margin-top:3px}