:root{
  --ink:#1b2420; --ink2:#5b6b62; --line:#e6ebe7; --bg:#fbfcfa; --card:#fff;
  --accent:#6aa72e; --accent-soft:#eef6e4; --warn:#b3261e; --warn-soft:#fdf0ee;
  --radius:16px; --shadow:0 1px 2px rgba(20,40,20,.05),0 8px 24px rgba(20,40,20,.06);
}
*{box-sizing:border-box;margin:0;padding:0}
html{scroll-behavior:smooth}
body{
  font-family:-apple-system,BlinkMacSystemFont,"Segoe UI",Roboto,"PingFang SC","Hiragino Sans GB","Microsoft YaHei","Noto Sans CJK SC",sans-serif;
  background:var(--bg);color:var(--ink);line-height:1.75;-webkit-font-smoothing:antialiased;
}
.wrap{max-width:1000px;margin:0 auto;padding:0 clamp(14px,4vw,28px)}

/* cover */
.cover{
  background:linear-gradient(135deg,var(--accent),color-mix(in srgb,var(--accent) 55%,#000 18%));
  color:#fff;border-radius:0 0 28px 28px;padding:clamp(36px,7vw,72px) 0 clamp(28px,5vw,48px);
  position:relative;overflow:hidden;
}
.cover::after{content:"";position:absolute;right:-80px;top:-80px;width:min(260px,38vw);height:min(260px,38vw);border-radius:50%;background:rgba(255,255,255,.10)}
.kicker{font-size:12.5px;letter-spacing:.14em;text-transform:uppercase;opacity:.85;margin-bottom:14px;font-weight:600}
.cover h1{font-size:clamp(26px,5vw,40px);line-height:1.25;font-weight:800;letter-spacing:-.01em}
.cover h1 .zh{display:block;font-size:.62em;font-weight:600;opacity:.9;margin-top:6px}
.cover .desc{margin-top:16px;max-width:640px;font-size:clamp(14px,2.4vw,16.5px);opacity:.95}
.cover .desc .zh{display:block;opacity:.82;font-size:.95em;margin-top:4px}
.objectives{margin-top:24px;display:grid;gap:10px;grid-template-columns:repeat(auto-fit,minmax(230px,1fr))}
.objectives div{background:rgba(255,255,255,.14);border:1px solid rgba(255,255,255,.22);border-radius:12px;padding:10px 14px;font-size:13.5px;backdrop-filter:blur(4px)}
.objectives b{display:block;font-size:11px;letter-spacing:.1em;text-transform:uppercase;opacity:.75;margin-bottom:2px}

/* toc */
.toc{position:sticky;top:0;z-index:50;background:rgba(251,252,250,.92);backdrop-filter:blur(10px);border-bottom:1px solid var(--line)}
.toc .wrap{display:flex;gap:8px;overflow-x:auto;padding-top:10px;padding-bottom:10px;scrollbar-width:none}
.toc .wrap::-webkit-scrollbar{display:none}
.toc a{white-space:nowrap;font-size:12.5px;font-weight:600;color:var(--ink2);text-decoration:none;border:1px solid var(--line);background:var(--card);border-radius:999px;padding:5px 13px;transition:.15s}
.toc a:hover{border-color:var(--accent);color:var(--accent)}
.toc a.on{background:var(--accent);border-color:var(--accent);color:#fff}

/* sections */
main{padding:clamp(24px,5vw,44px) 0 20px}
.phase{scroll-margin-top:64px;margin-bottom:clamp(28px,5vw,44px)}
.phase-head{display:flex;align-items:baseline;gap:10px;margin-bottom:14px;border-bottom:2px solid var(--line);padding-bottom:10px}
.phase-num{flex:none;background:var(--accent);color:#fff;font-weight:800;font-size:12.5px;border-radius:8px;padding:3px 9px;letter-spacing:.04em}
.phase-head h2{font-size:clamp(19px,3.2vw,24px);font-weight:800}
.phase-head .zh{font-size:clamp(13px,2vw,15px);color:var(--ink2);font-weight:600}

.card{background:var(--card);border:1px solid var(--line);border-radius:var(--radius);box-shadow:var(--shadow);padding:clamp(16px,3vw,24px);margin-bottom:14px}
.card h3{font-size:13px;letter-spacing:.08em;text-transform:uppercase;color:var(--accent);margin-bottom:10px;display:flex;align-items:center;gap:8px}
.concept{font-size:clamp(14.5px,2.6vw,16px)}
.concept .zh{display:block;color:var(--ink2);margin-top:6px;font-size:.95em}

.rules{display:grid;gap:0}
.rule{display:grid;grid-template-columns:110px 1fr;gap:4px 14px;padding:11px 4px;border-bottom:1px dashed var(--line)}
.rule:last-child{border-bottom:0}
.rule b{grid-column:1;grid-row:1/3;font-size:12.5px;color:var(--accent);background:var(--accent-soft);align-self:start;border-radius:8px;padding:3px 10px;text-align:center}
.rule .en{font-size:14.5px}
.rule .zh{color:var(--ink2);font-size:13.5px}

.ex{border-left:3px solid var(--accent);padding:10px 14px;background:var(--accent-soft);border-radius:0 10px 10px 0;margin-bottom:8px}
.ex .en{font-weight:600;font-size:14.5px}
.ex .zh{color:var(--ink2);font-size:13.5px}

.mistakes{background:var(--warn-soft);border:1px solid #f3d3cf}
.mistakes h3{color:var(--warn)}
.mistake{padding:9px 12px;border-bottom:1px dashed #f0c9c4;font-size:13.8px}
.mistake:last-child{border-bottom:0}
.mistake .zh{display:block;color:#8a5a55;font-size:13px;margin-top:2px}

/* practice */
.practice .p-q{margin-bottom:12px;border:1px solid var(--line);border-radius:12px;overflow:hidden;background:var(--card)}
.practice details summary{cursor:pointer;list-style:none;padding:14px 16px;display:flex;gap:10px;align-items:flex-start}
.practice details summary::-webkit-details-marker{display:none}
.practice details[open] summary{border-bottom:1px dashed var(--line)}
.practice .qnum{flex:none;background:var(--ink);color:#fff;font-size:11px;font-weight:700;border-radius:7px;padding:3px 8px;margin-top:3px}
.practice .qtext{font-size:14.5px;font-weight:600}
.practice .opts{padding:8px 16px 14px}
.practice .opt{display:block;width:100%;text-align:left;font:inherit;font-size:13.8px;padding:7px 10px;border-radius:8px;margin-top:6px;background:#f4f7f4;border:1px solid var(--line);cursor:pointer}
.practice .opt:focus-visible,.toc a:focus-visible,.nav-prev-next a:focus-visible,.toplink:focus-visible{outline:3px solid #1b2420;outline-offset:2px}
.practice .opt[aria-pressed="true"]{border-color:var(--accent);box-shadow:0 0 0 2px color-mix(in srgb,var(--accent) 25%,transparent)}
.practice .opt.right{background:#e8f5dc;border-color:#b7d992;font-weight:700}
.practice .opt.right::after{content:" ✓ 正确答案";color:var(--accent);font-size:12px;font-weight:700}
.practice .hint{padding:10px 16px;font-size:12.5px;color:var(--ink2);border-top:1px dashed var(--line);background:#fafcfa}

/* footer */
footer{border-top:1px solid var(--line);margin-top:20px;padding:26px 0 40px}
.nav-prev-next{display:flex;gap:12px;flex-wrap:wrap;margin-bottom:22px}
.nav-prev-next a{flex:1;min-width:200px;background:var(--card);border:1px solid var(--line);border-radius:14px;padding:14px 18px;text-decoration:none;color:var(--ink);box-shadow:var(--shadow);transition:.15s}
.nav-prev-next a:hover{border-color:var(--accent);transform:translateY(-1px)}
.nav-prev-next .dir{font-size:11px;letter-spacing:.1em;text-transform:uppercase;color:var(--ink2)}
.nav-prev-next .t{font-weight:700;font-size:14.5px;margin-top:2px}
.credit{font-size:12.5px;color:var(--ink2);text-align:center}
.credit a{color:var(--accent);text-decoration:none;font-weight:600}
.toplink{display:inline-block;margin-top:10px;font-size:12.5px;color:var(--accent);text-decoration:none;font-weight:600}

@media print{
  .toc,footer .nav-prev-next,.toplink{display:none}
  body{background:#fff}
  .cover{border-radius:0}
  .phase{page-break-inside:avoid}
}
@media (max-width:640px){
  .rule{grid-template-columns:1fr}
  .rule b{grid-row:auto;justify-self:start;margin-bottom:2px}
  .objectives{grid-template-columns:1fr}
}

/* GramLingo landing-page visual language */
@font-face{font-family:Baloo2;src:url('assets/fonts/baloo2-700.woff2') format('woff2');font-weight:700;font-display:swap}
@font-face{font-family:Baloo2;src:url('assets/fonts/baloo2-800.woff2') format('woff2');font-weight:800;font-display:swap}
@font-face{font-family:DMSans;src:url('assets/fonts/dmsans-400.woff2') format('woff2');font-weight:400;font-display:swap}
@font-face{font-family:DMSans;src:url('assets/fonts/dmsans-600.woff2') format('woff2');font-weight:600;font-display:swap}
:root{--ink:#2d1b10;--ink2:#6f5b4d;--line:#e8d5c4;--bg:#fff5ee;--card:#fff;--accent:#ff8c42;--accent-soft:#fff0e5;--warn:#b94b4b;--warn-soft:#fff1ed;--radius:20px;--shadow:0 3px 0 rgba(45,27,16,.1),0 12px 28px rgba(117,70,40,.08)}
body{font-family:DMSans,-apple-system,BlinkMacSystemFont,"Segoe UI","PingFang SC","Microsoft YaHei",sans-serif;background:var(--bg);color:var(--ink)}
h1,h2,h3{font-family:Baloo2,DMSans,sans-serif}
.cover{background:linear-gradient(135deg,#ff8c42,#e86f35);color:var(--ink);border-radius:0 0 32px 32px}
.cover::after{right:clamp(18px,9vw,120px);top:28px;width:130px;height:130px;background:url('assets/gramlingo-logo.png') center/contain no-repeat;opacity:.95;transform:rotate(5deg)}
.cover::before{content:"";position:absolute;inset:auto -80px -130px auto;width:340px;height:340px;border-radius:50%;background:rgba(255,255,255,.2)}
.cover h1{font-size:clamp(30px,5vw,48px);line-height:1.1}
.objectives div{background:rgba(255,255,255,.55);border:2px solid rgba(45,27,16,.12);border-radius:14px;box-shadow:0 3px 0 rgba(45,27,16,.08)}
.toc{background:rgba(255,250,246,.94);border-color:var(--line)}
.toc a{border:2px solid var(--line)}
.toc a.on{background:var(--accent);border-color:var(--ink);color:var(--ink)}
.phase-num{background:var(--accent);color:var(--ink);border:2px solid var(--ink);border-radius:999px}
.card{border:2px solid var(--line);box-shadow:var(--shadow)}
.rule b{color:var(--ink);background:var(--accent-soft);border:1px solid var(--line);border-radius:999px}
.ex{border:1px solid #ffd2b2;border-left:5px solid var(--accent);background:var(--accent-soft);border-radius:0 12px 12px 0}
.practice .opt{background:#fffaf6;border:2px solid var(--line);border-radius:10px}
.practice .opt[aria-pressed="true"]{border-color:var(--accent);box-shadow:0 0 0 3px rgba(255,140,66,.22)}
.nav-prev-next a{border:2px solid var(--line)}
@media (max-width:640px){.cover::after{right:12px;top:20px;width:84px;height:84px;opacity:.7}}
.hub .cover{padding-bottom:clamp(34px,6vw,58px)}
.hub .cover h1{max-width:none}
.hub .cover .sub{max-width:680px;margin-top:14px}
.hub .grid{display:grid;grid-template-columns:repeat(auto-fit,minmax(260px,1fr));gap:18px;padding:clamp(26px,5vw,48px) 0}
.hub .module-card{display:block;overflow:hidden;background:var(--card);border:2px solid var(--line);border-radius:20px;color:var(--ink);text-decoration:none;box-shadow:var(--shadow);transition:transform .15s,box-shadow .15s,border-color .15s}
.hub .module-card:hover{transform:translateY(-3px);border-color:var(--accent);box-shadow:0 5px 0 rgba(45,27,16,.12),0 18px 34px rgba(117,70,40,.12)}
.hub .module-card img{display:block;width:100%;aspect-ratio:3/1.25;object-fit:cover}
.hub .module-card-body{padding:16px 18px 18px}
.hub .module-card-body .num{font-size:11px;letter-spacing:.1em;text-transform:uppercase;color:var(--accent);font-weight:700}
.hub .module-card-body h2{font-size:20px;line-height:1.2;margin-top:6px}
.hub .module-card-body .zh{display:block;color:var(--ink2);font-size:15px;margin-top:3px}
.hub .module-card-body p{margin-top:9px;color:var(--ink2);font-size:13.5px}
.hub footer{border-top:1px solid var(--line);padding:24px 0 40px;text-align:center;color:var(--ink2);font-size:12.5px}
.hub footer a{color:var(--accent);font-weight:700;text-decoration:none}
.lesson-nav{height:64px;display:flex;align-items:center;justify-content:space-between;padding:0 clamp(16px,4vw,32px);background:rgba(255,245,238,.92);backdrop-filter:blur(12px);-webkit-backdrop-filter:blur(12px);border-bottom:1px solid var(--line);position:sticky;top:0;z-index:100}
.cover::after{display:none}
.lesson-nav{height:70px;padding:0 clamp(18px,5vw,52px);gap:18px}.lesson-brand img{width:126px}.lesson-nav-links{gap:4px;flex:1;justify-content:center}.lesson-nav-link{border:2px solid transparent;color:var(--ink);font-size:13px;padding:8px 13px}.lesson-nav-link:hover{border-color:var(--ink);background:#fff}.lesson-nav-link--active{border-color:var(--ink);background:var(--card)}.lesson-nav-link--cta{background:var(--accent);border-color:var(--ink);box-shadow:0 3px 0 var(--ink)}.lesson-nav-link--cta:hover{background:#ffb788}.lesson-language{display:flex;align-items:center;border:2px solid var(--ink);border-radius:999px;background:var(--card);overflow:hidden;font-size:12px;font-weight:700}.lesson-language span{padding:7px 9px}.lesson-language--active{background:var(--accent)}
.cover{background:radial-gradient(circle at 88% 20%,rgba(255,183,136,.35),transparent 28%),var(--bg);color:var(--ink);border:0}.cover .kicker{display:inline-block;border:2px solid var(--accent);border-radius:999px;padding:6px 12px;opacity:1;letter-spacing:.1em}.cover h1{color:var(--ink)}.cover .desc{color:var(--ink2)}.objectives div{background:var(--card);border:2px solid var(--ink);box-shadow:3px 3px 0 var(--ink)}.hub .cover{padding-top:clamp(34px,7vw,70px)}.hub-gramlin{position:absolute;right:clamp(24px,12vw,160px);bottom:-8px;width:150px;filter:drop-shadow(0 5px 0 rgba(45,27,16,.15));animation:lesson-float 4s ease-in-out infinite}.hub .cover .wrap{position:relative}.hub .cover h1{max-width:700px}.hub .cover .sub{max-width:680px}.hub .module-card{border:2px solid var(--ink);box-shadow:4px 4px 0 var(--ink)}.hub .module-card:hover{border-color:var(--ink);box-shadow:6px 7px 0 var(--ink);transform:translate(-2px,-4px)}
.lesson-brand{display:inline-flex;align-items:center;height:48px}.lesson-brand img{display:block;width:132px;height:auto}.lesson-nav-links{display:flex;align-items:center;gap:8px}.lesson-nav-link{color:var(--ink);font-size:13px;font-weight:600;padding:8px 12px;border-radius:999px;transition:background .15s,color .15s}.lesson-nav-link:hover,.lesson-nav-link--active{background:var(--accent-soft);color:var(--ink)}
.hub .cover{border-radius:0 0 32px 32px}.hub .cover::after{background:url('assets/gramlingo-logo.png') center/contain no-repeat}.hub .module-gallery-section{padding:clamp(40px,8vw,72px) 0}.hub .gallery-wrap{max-width:980px}.hub .module-gallery{gap:16px;padding:8px 4px 14px}.hub .module-card{width:260px;border-radius:10px;border:1px solid #f0e5d8;box-shadow:none}.hub .module-card:hover{transform:translateY(-4px);box-shadow:0 8px 24px rgba(45,27,16,.1)}.hub .module-card-cover{aspect-ratio:3/4}.hub .module-card-body h2{font-family:Baloo2,DMSans,sans-serif;font-size:16px;min-height:2.6em;margin:0 0 4px}.hub .module-card-body{padding:16px}.hub .module-card-body p{display:-webkit-box;-webkit-line-clamp:2;-webkit-box-orient:vertical;overflow:hidden}.hub .module-card-body p.zh{margin-top:3px}.lesson-nav-link:focus-visible,.lesson-brand:focus-visible{outline:3px solid var(--accent);outline-offset:2px}
.cover-art{animation:lesson-float 4s ease-in-out infinite}.lesson-brand img{animation:logo-settle .6s var(--ease-bounce)}
@keyframes lesson-float{0%,100%{transform:translateY(0) rotate(0)}50%{transform:translateY(-8px) rotate(2deg)}}
@keyframes logo-settle{from{opacity:0;transform:translateY(-5px) scale(.96)}to{opacity:1;transform:none}}
@media (prefers-reduced-motion:reduce){.cover-art,.lesson-brand img{animation:none}}
@media (max-width:900px){.lesson-nav-links{overflow-x:auto;justify-content:flex-end}.lesson-nav-link{white-space:nowrap}.lesson-language{display:none}.hub-gramlin{right:18px;width:110px}}
@media (max-width:640px){.lesson-nav{height:58px;padding:0 10px}.lesson-brand img{width:104px}.lesson-nav-links{gap:0}.lesson-nav-link{font-size:11px;padding:7px 8px}.lesson-nav-link:not(.lesson-nav-link--active):not(.lesson-nav-link--cta){display:none}.hub-gramlin{display:none}.cover h1{padding-right:0}}
@media (max-width:640px){.hub .grid{grid-template-columns:1fr}.hub .module-card img{aspect-ratio:3/1.1}}