/* Học Claude AI · giao diện trang học, phong cách cổ điển
   Giấy ngà, mực nâu đen, đỏ rượu vang và nét vàng đồng; tiêu đề kiểu chữ sách giáo khoa (HC Schola),
   thân bài chữ có chân (HC Book). Khung video giữ đúng màu và chữ của giao diện Claude.
   Mọi kích thước tính theo rem để nút "Cỡ chữ" phóng to, thu nhỏ được cả trang. */

:root{
  --paper:#f3eee3; --sheet:#fbf8f1; --ink:#26221d; --ink2:#5f574b; --wine:#7a2333; --wine2:#5a1726;
  --gold:#9a7838; --line:#d8cdb9; --soft:#ede4d1; --hl:#f2e3b8; --shadow:rgba(60,40,20,.10);
  --c-bg:#faf9f5; --c-side:#f5f4ee; --c-card:#ffffff; --c-fg:#141413; --c-mu:#6b6a64; --c-bd:#e6e3d9; --c-us:#f0eee6; --c-ac:#c96442;
  --display:"HC Schola","Century Schoolbook","Georgia",serif;
  --text:"HC Book","Lora","Georgia","Times New Roman","PingFang SC","Microsoft YaHei","Noto Serif CJK SC",serif;
  --ui:"Inter",system-ui,-apple-system,"Segoe UI",Roboto,"PingFang SC","Microsoft YaHei",sans-serif;
  --fs:1; --chrome:128px; --left:56%; --top:46%;
  color-scheme:light;
}
@media (prefers-color-scheme:dark){:root:not([data-theme="light"]){
  --paper:#16130f; --sheet:#1f1b15; --ink:#eee6d6; --ink2:#b8ac96; --wine:#de8f9a; --wine2:#ecabb3;
  --gold:#c9a660; --line:#3b3328; --soft:#2a241b; --hl:#3e331b; --shadow:rgba(0,0,0,.4);
  --c-bg:#262624; --c-side:#1f1e1d; --c-card:#30302e; --c-fg:#f5f4ef; --c-mu:#a6a39a; --c-bd:#3d3c38; --c-us:#141413; --c-ac:#d97757;
  color-scheme:dark}}
:root[data-theme="dark"]{
  --paper:#16130f; --sheet:#1f1b15; --ink:#eee6d6; --ink2:#b8ac96; --wine:#de8f9a; --wine2:#ecabb3;
  --gold:#c9a660; --line:#3b3328; --soft:#2a241b; --hl:#3e331b; --shadow:rgba(0,0,0,.4);
  --c-bg:#262624; --c-side:#1f1e1d; --c-card:#30302e; --c-fg:#f5f4ef; --c-mu:#a6a39a; --c-bd:#3d3c38; --c-us:#141413; --c-ac:#d97757;
  color-scheme:dark}

*,*::before,*::after{box-sizing:border-box}
html{font-size:calc(var(--fs) * 100%);scroll-behavior:smooth;scroll-padding-top:6rem;-webkit-text-size-adjust:100%}
body{margin:0;background:var(--paper);color:var(--ink);font:400 1.125rem/1.7 var(--text);-webkit-font-smoothing:antialiased;font-variant-numeric:oldstyle-nums}
body.in-lesson{overflow:hidden}
[hidden]{display:none!important}
img,svg,canvas{max-width:100%}
a{color:var(--wine);text-underline-offset:.18em}
h1,h2,h3{font-family:var(--display);font-weight:700;line-height:1.18;text-wrap:balance;margin:0;color:var(--ink)}
p{margin:0}
.wrap{max-width:72rem;margin:0 auto;padding-left:max(1.1rem,env(safe-area-inset-left,0px));padding-right:max(1.1rem,env(safe-area-inset-right,0px))}
.muted{color:var(--ink2)}
.sr{position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap}
.skip{position:absolute;left:-999px;top:.5rem;background:var(--wine);color:#fff;padding:.5rem .9rem;z-index:60}
.skip:focus{left:.8rem}
:focus-visible{outline:2px solid var(--gold);outline-offset:3px}
.view{animation:viewin .28s ease}
@keyframes viewin{from{opacity:0;transform:translateY(.4rem)}to{opacity:1;transform:none}}

/* hoa văn ngăn cách: hai nét kẻ và một ô thoi ở giữa */
.orn{display:flex;align-items:center;gap:.8rem;color:var(--gold);margin:1.4rem 0;max-width:22rem}
.orn::before,.orn::after{content:"";flex:1;border-top:1px solid currentColor}
.orn span{width:.5rem;height:.5rem;transform:rotate(45deg);border:1px solid currentColor;flex:none}

/* ---------- nút ---------- */
.btn{font:600 1rem/1.2 var(--text);display:inline-flex;align-items:center;justify-content:center;gap:.5rem;min-height:3rem;padding:.75rem 1.3rem;border-radius:3px;
  border:1px solid transparent;cursor:pointer;text-decoration:none;letter-spacing:.01em;transition:background .15s ease,transform .1s ease}
.btn.primary{background:var(--wine);color:#fff8ee;border-color:var(--wine);box-shadow:inset 0 0 0 2px var(--wine),inset 0 0 0 3px rgba(255,248,238,.45)}
.btn.primary:hover{background:var(--wine2)}
:root[data-theme="dark"] .btn.primary{color:#1c1410}
@media (prefers-color-scheme:dark){:root:not([data-theme="light"]) .btn.primary{color:#1c1410}}
.btn.primary:active{transform:translateY(1px)}
.btn.quiet{background:transparent;color:var(--wine);border-color:var(--line)}
.btn.quiet:hover{background:var(--soft)}
.btn.big{min-height:3.4rem;padding:.85rem 1.6rem;font-size:1.06rem}
.btn:disabled{opacity:.45;cursor:not-allowed;transform:none}
.link{font:inherit;background:none;border:0;padding:0;color:var(--wine);text-decoration:underline;cursor:pointer}

/* ---------- đầu trang ---------- */
.notice{background:var(--wine);color:#fff8ee;text-align:center;padding:.6rem 1.1rem;font-weight:600;font-size:.98rem}
:root[data-theme="dark"] .notice{color:#1c1410}
@media (prefers-color-scheme:dark){:root:not([data-theme="light"]) .notice{color:#1c1410}}
.notice.preview{background:var(--hl);color:var(--ink)}
header.site{position:sticky;top:0;z-index:30;background:color-mix(in srgb,var(--paper) 93%,transparent);backdrop-filter:blur(8px);border-bottom:3px double var(--line)}
.site-in{display:flex;align-items:center;gap:.6rem 1.2rem;min-height:4rem;flex-wrap:wrap;padding-block:.45rem}
.brand{display:flex;align-items:center;gap:.6rem;font:700 1.3rem/1 var(--display);color:var(--ink);text-decoration:none}
.seal{width:2.2rem;height:2.2rem;border-radius:50%;display:grid;place-items:center;font:700 1.15rem/1 var(--display);color:var(--wine);
  border:1.5px solid var(--gold);box-shadow:inset 0 0 0 3px var(--paper),inset 0 0 0 4px var(--gold)}
.site-nav{margin-left:auto}
.site-nav a{font-weight:600;color:var(--ink);text-decoration:none;font-size:1rem;border-bottom:1px solid transparent}
.site-nav a:hover{border-color:var(--wine);color:var(--wine)}
.fs{display:flex;border:1px solid var(--line);border-radius:3px;overflow:hidden}
.fs-b{font:700 .85rem/1 var(--display);min-width:2.5rem;min-height:2.4rem;padding:0 .5rem;background:var(--sheet);color:var(--ink);border:0;cursor:pointer;display:inline-flex;align-items:baseline;justify-content:center;gap:1px}
.fs-b+.fs-b{border-left:1px solid var(--line)}
.fs-b.mid{font-size:1rem}.fs-b.big{font-size:1.15rem}
.fs-b:hover{background:var(--soft)}
.fs-b:disabled{opacity:.4;cursor:default}
.langs{display:flex;gap:.35rem}
.lb{font:500 .85rem/1 var(--ui);display:inline-flex;align-items:center;gap:.35rem;min-height:2.4rem;padding:.3rem .6rem;border-radius:3px;border:1px solid var(--line);background:var(--sheet);color:var(--ink);cursor:pointer}
.lb[aria-pressed="true"]{border-color:var(--wine);box-shadow:inset 0 0 0 1px var(--wine);font-weight:700}
.fl{width:1.25rem;height:.875rem;box-shadow:0 0 0 1px rgba(0,0,0,.15)}

/* ---------- hero ---------- */
.hero{padding-block:3.4rem 2.6rem}
.hero-in{display:grid;grid-template-columns:minmax(0,1.1fr) minmax(0,.9fr);gap:3.2rem;align-items:center}
.tag{font-style:italic;color:var(--wine);font-size:1.05rem}
.hero h1{font-size:clamp(2.4rem,5vw,3.9rem);margin:.7rem 0 0;letter-spacing:-.005em}
.sub{font-size:1.18rem;max-width:34em}
.who{color:var(--ink2);font-style:italic;margin-top:.7rem;max-width:34em}
.cta-row{display:flex;gap:.8rem;flex-wrap:wrap;margin-top:1.8rem}
.byline{margin-top:1.4rem;color:var(--ink2);font-size:1rem;letter-spacing:.02em}
.plate{margin:0;padding:1.1rem 1.1rem .8rem;background:var(--sheet);border:1px solid var(--line);box-shadow:0 0 0 5px var(--paper),0 0 0 6px var(--line),0 1.2rem 2.4rem var(--shadow)}
.plate figcaption{font-style:italic;color:var(--ink2);text-align:center;font-size:.92rem;margin-top:.7rem}
.demo-win{background:var(--c-bg);color:var(--c-fg);border:1px solid var(--c-bd);border-radius:12px;overflow:hidden;font-family:var(--ui)}
.demo-top{display:flex;align-items:center;gap:.35rem;padding:.65rem .8rem;border-bottom:1px solid var(--c-bd);background:var(--c-side);font-size:.85rem}
.demo-top b{margin-left:.5rem}
.dot{width:.6rem;height:.6rem;border-radius:50%;background:var(--c-bd)}
.demo-chat{display:flex;flex-direction:column;gap:.7rem;padding:1rem .9rem;min-height:12rem;font-size:.92rem}
.bub{max-width:88%;padding:.6rem .85rem;border-radius:14px;line-height:1.5}
.bub.u{align-self:flex-end;background:var(--c-us)}
.bub.c{align-self:flex-start;background:var(--c-card);border:1px solid var(--c-bd)}
.bub:empty{display:none}
.bub.c{animation:none}
.demo.typing .bub.c{animation:fadein .5s ease}
@keyframes fadein{from{opacity:0;transform:translateY(.3rem)}to{opacity:1;transform:none}}
.demo-in{margin:0 .8rem .8rem;border:1px solid var(--c-bd);border-radius:14px;padding:.6rem .85rem;color:var(--c-mu);font-size:.85rem;background:var(--c-card)}

/* ---------- cách học ---------- */
.how{padding-block:.6rem 2.2rem}
.how-list{list-style:none;counter-reset:how;margin:0;padding:1.4rem 0 0;border-top:1px solid var(--line);display:grid;grid-template-columns:repeat(3,minmax(0,1fr));gap:1.4rem}
.how-list li{counter-increment:how;display:grid;grid-template-columns:auto 1fr;column-gap:.9rem;align-items:baseline}
.how-list li::before{content:counter(how,upper-roman) ".";grid-row:span 2;font:700 1.35rem/1 var(--display);color:var(--wine);min-width:2.2rem}
.how-list b{font-size:1.06rem}
.how-list span{color:var(--ink2);font-size:1rem}

/* ---------- mục lục ---------- */
.toc{padding-block:1rem 3rem;outline:none}
.toc-sheet{background:var(--sheet);border:1px solid var(--line);box-shadow:0 0 0 5px var(--paper),0 0 0 6px var(--line);padding:2.2rem clamp(1rem,4vw,3rem) 2.4rem}
.toc-head{text-align:center;margin-bottom:1.8rem}
.toc-head h2{font-size:clamp(1.9rem,3.4vw,2.6rem);margin-bottom:.35rem}
.prog{display:flex;align-items:center;gap:.8rem;justify-content:center;margin-top:1rem;font-weight:600;font-size:.98rem}
.bar{width:12rem;height:.4rem;background:var(--soft);border:1px solid var(--line);overflow:hidden;flex:none}
.bar i{display:block;height:100%;width:0;background:var(--wine);transition:width .5s ease}
.part{margin-top:1.6rem}
.part-h{display:flex;align-items:baseline;justify-content:space-between;gap:.8rem;flex-wrap:wrap;border-bottom:1px solid var(--ink);padding-bottom:.35rem;margin-bottom:.3rem}
.part-h h3{font-size:1.28rem}
.sticker{font-style:italic;color:var(--wine);font-size:.92rem}
.lessons{list-style:none;margin:0;padding:0}
.row{display:grid;grid-template-columns:2.4rem minmax(0,1fr) auto;align-items:baseline;gap:0 .9rem;padding:.7rem .2rem;border:0;border-bottom:1px dotted var(--line);
  width:100%;background:none;font:inherit;color:inherit;text-align:left;cursor:pointer;transition:background .15s ease}
.row:hover:not(:disabled){background:color-mix(in srgb,var(--soft) 70%,transparent)}
.row:disabled{cursor:not-allowed}
.row .no{font:700 1.1rem/1.3 var(--display);color:var(--wine);text-align:right}
.row .tt{font-weight:600;line-height:1.4;display:block}
.row .gl{display:block;color:var(--ink2);font-size:.92rem;font-style:italic;line-height:1.45}
.st{font:600 .9rem/1 var(--text);white-space:nowrap}
.st.done{color:var(--wine)}
.st.done::before{content:"✓ ";font-family:var(--ui)}
.st.now{color:var(--wine);border-bottom:1px solid var(--wine);padding-bottom:2px}
.st.lock{color:var(--ink2);font-style:italic;font-weight:400}
.row:disabled .tt,.row:disabled .no{opacity:.55}

/* ---------- bài học: hai khung cuộn riêng ---------- */
.lesson-bar{background:var(--sheet);border-bottom:1px solid var(--line)}
.lesson-bar-in{display:flex;align-items:center;gap:1rem;min-height:3rem}
.back{font-weight:600;text-decoration:none;white-space:nowrap}
.back::before{content:"‹ ";font-family:var(--ui);font-size:1.15em}
.lesson-count{color:var(--ink2);font-size:.95rem;white-space:nowrap;margin-left:auto}
.split{display:grid;grid-template-columns:var(--left) .75rem minmax(0,1fr);height:calc(100dvh - var(--chrome));max-width:90rem;margin:0 auto}
.pane{overflow-y:auto;overscroll-behavior:contain;padding:1.8rem clamp(1rem,2.6vw,2.4rem) 3rem;outline:none;scrollbar-width:thin;scrollbar-color:var(--gold) transparent}
.pane::-webkit-scrollbar{width:.7rem}
.pane::-webkit-scrollbar-thumb{background:color-mix(in srgb,var(--gold) 70%,transparent);border-radius:1rem;border:3px solid var(--paper)}
.pane::-webkit-scrollbar-track{background:transparent}
.pane-lesson{background:var(--paper)}
.pane-quiz{background:var(--sheet);border-left:1px solid var(--line)}
.split-bar{position:relative;cursor:col-resize;background:var(--paper);touch-action:none;display:flex;align-items:center;justify-content:center}
.split-bar::before{content:"";position:absolute;top:0;bottom:0;left:50%;border-left:3px double var(--line);transform:translateX(-50%)}
.split-bar span{position:relative;width:.55rem;height:2.6rem;border:1px solid var(--gold);background:var(--sheet);border-radius:2px}
.split-bar:hover span,.split-bar:focus-visible span,.split-bar.drag span{background:var(--gold)}
.kicker{font-style:italic;color:var(--wine)}
.pane-lesson h1{font-size:clamp(1.8rem,3vw,2.5rem);margin:.3rem 0 .6rem;outline:none}
.goal{color:var(--ink2);max-width:38em}
.pane h2{font-size:1.3rem;margin:2rem 0 .9rem}
.pane h2:first-child{margin-top:0}
.steps{list-style:none;counter-reset:st;margin:0;padding:0;display:flex;flex-direction:column;gap:.7rem;max-width:40em}
.steps li{counter-increment:st;display:grid;grid-template-columns:2rem 1fr;gap:.6rem;align-items:baseline}
.steps li::before{content:counter(st) ".";font:700 1.05rem/1 var(--display);color:var(--wine);text-align:right}
.practice{margin-top:1.3rem;max-width:40em;padding:.9rem 1.1rem;background:var(--hl);border-left:3px solid var(--gold)}
.practice b{display:block;font-family:var(--display);font-size:1.02rem;margin-bottom:.15rem}

/* câu hỏi nhanh: kiểu đề thi in */
.quiz-intro{color:var(--ink2);font-style:italic;font-size:.98rem;margin:-.4rem 0 1rem}
.q{display:flex;flex-direction:column;gap:1.3rem}
.qblk{display:flex;flex-direction:column;gap:.5rem;padding-bottom:1.2rem;border-bottom:1px dotted var(--line)}
.qn{font:700 .95rem/1 var(--display);color:var(--wine)}
.qq{font-weight:600;font-size:1.06rem;line-height:1.5}
.qb{font:400 1rem/1.45 var(--text);text-align:left;width:100%;min-height:2.9rem;padding:.6rem .9rem .6rem 2.6rem;border-radius:3px;border:1px solid var(--line);background:var(--paper);color:var(--ink);cursor:pointer;position:relative}
.qb::before{content:attr(data-letter) ".";position:absolute;left:.85rem;top:.6rem;font:700 1rem/1.45 var(--display);color:var(--wine)}
.qb:hover:not(:disabled){border-color:var(--wine);background:var(--sheet)}
.qb:disabled{cursor:default}
.qb.ok{border-color:var(--wine);background:color-mix(in srgb,var(--wine) 9%,var(--sheet));font-weight:600}
.qb.ok::after{content:"✓";position:absolute;right:.9rem;top:50%;transform:translateY(-50%);color:var(--wine);font:700 1.2rem/1 var(--ui);animation:pop .3s ease}
@keyframes pop{0%{transform:translateY(-50%) scale(.4);opacity:0}100%{transform:translateY(-50%) scale(1);opacity:1}}
.qb.no{color:var(--ink2);text-decoration:line-through;text-decoration-color:var(--wine);opacity:.75}
.fb{font-size:.97rem;min-height:1.4em}
.fb.good{color:var(--wine);font-style:italic}
.fb.bad{color:var(--wine);font-weight:600}
.okb{border:1px solid var(--wine);box-shadow:inset 0 0 0 3px var(--sheet),inset 0 0 0 4px var(--wine);color:var(--wine);padding:.9rem 1.1rem;font-weight:600;text-align:center;animation:fadein .35s ease}
.pbox.pq{margin-top:1.8rem;padding:1.3rem;background:var(--paper);border:1px solid var(--line)}
.pbox.pq h2{margin-top:0}
.pn{display:flex;gap:.8rem;justify-content:space-between;flex-wrap:wrap;margin-top:1.8rem}
.hint{color:var(--ink2);font-style:italic;font-size:.95rem;margin-top:.6rem}
.hint:empty{display:none}
.finish{margin-top:1rem}

/* ---------- khung video mô phỏng Claude (giữ đúng giao diện Claude) ---------- */
.vid{max-width:46rem;font-family:var(--ui)}
.scr{position:relative;border:1px solid var(--c-bd);border-radius:12px;overflow:hidden;background:var(--c-bg);color:var(--c-fg);box-shadow:0 .6rem 1.4rem var(--shadow)}
.bd{position:relative}
.app{display:flex;min-height:24rem;background:var(--c-card);font-size:.8rem}
.sb{flex:0 0 30%;background:var(--c-side);border-right:1px solid var(--c-bd);padding:.6rem .5rem;display:flex;flex-direction:column;gap:2px}
.sb>div{padding:.35rem .5rem;border-radius:8px}
.sb .on{background:var(--c-bd);font-weight:700}
.nw{font-weight:700;background:var(--c-bd);margin-bottom:.35rem}
.sec{color:var(--c-mu);font-size:.7rem;margin-top:.6rem;padding-left:.5rem;font-weight:600}
.rc{white-space:nowrap;overflow:hidden;text-overflow:ellipsis}
.mn{flex:1;min-width:0;display:flex;flex-direction:column;background:var(--c-bg)}
.top{display:flex;justify-content:space-between;align-items:center;padding:.5rem .9rem;border-bottom:1px solid var(--c-bd)}
.top .tt{font-weight:700;font-size:.92rem}
.shr{font-size:.8rem;border:1px solid var(--c-bd);border-radius:8px;padding:.25rem .6rem}
.chatarea{flex:1;padding:.75rem .9rem;display:flex;flex-direction:column;gap:.5rem;min-height:12rem}
.ib{margin:0 .9rem .25rem;border:1px solid var(--c-bd);border-radius:16px;background:var(--c-card);padding:.6rem .9rem;display:flex;gap:.6rem;align-items:center;color:var(--c-mu);font-size:.85rem}
.ib .ph{flex:1}
.ib .mdl{font-size:.75rem;border:1px solid var(--c-bd);border-radius:8px;padding:2px .5rem;color:var(--c-fg)}
.ft{font-size:.66rem;color:var(--c-mu);text-align:center;padding:.25rem .5rem .5rem}
.hh{font-weight:700;font-size:1.05rem}
.bt{align-self:flex-start;background:var(--c-ac);color:#fff;border-radius:8px;padding:.45rem .9rem;font-weight:700;font-size:.9rem}
.ip{border:1px solid var(--c-bd);background:var(--c-card);border-radius:8px;padding:.5rem .6rem;min-height:2.4em;font-size:.92rem}
.tx{color:var(--c-mu);font-size:.92rem}
.m{max-width:88%;padding:.55rem .8rem;border-radius:12px;font-size:.92rem}
.m.u{align-self:flex-end;background:var(--c-us)}
.m.c{align-self:flex-start;background:var(--c-card);border:1px solid var(--c-bd)}
.rw{display:flex;gap:.35rem;flex-wrap:wrap}
.tb{padding:.3rem .7rem;border-radius:8px;font-size:.88rem;border:1px solid var(--c-bd)}
.tb.on{background:var(--c-bd);font-weight:700}
.cd2{background:color-mix(in srgb,var(--c-ac) 14%,var(--c-card));border-radius:12px;padding:.6rem .75rem;display:flex;flex-direction:column;gap:.35rem;align-items:flex-start;font-size:.9rem}
.gt{font-weight:700}
.gd{color:var(--c-mu);font-size:.85rem}
.clk{outline:3px solid #e8b04b;outline-offset:2px}
.cur{position:absolute;width:18px;height:18px;border-radius:50%;background:#e8b04b;border:2px solid #26221d;opacity:0;transition:left .8s ease,top .8s ease,opacity .3s;pointer-events:none;z-index:3}
.cap{font:italic .85rem/1.4 var(--text);color:var(--ink2);margin:.6rem 2px 2px}
.subt{margin:2px 2px 0;font:500 1.02rem/1.55 var(--text);min-height:3.2em;color:var(--ink)}
.pbar{height:.3rem;background:var(--soft);margin:.6rem 0;overflow:hidden}
.pbar i{display:block;height:100%;width:0;background:var(--wine);transition:width .4s}
.ctl{display:flex;gap:.5rem;flex-wrap:wrap}
.ctl .btn{min-height:2.7rem;padding:.55rem 1rem;font-size:.95rem}

/* ---------- chân trang và tác giả ---------- */
.site-foot{border-top:3px double var(--line);background:var(--sheet)}
body.in-lesson .site-foot{display:none}
.foot-in{display:flex;flex-direction:column;gap:.7rem;padding-block:2.4rem 3rem}
.foot-in>p{max-width:52em}
.about{display:grid;grid-template-columns:auto minmax(0,1fr);gap:1.8rem;align-items:start;margin-bottom:.4rem}
.about-text{display:flex;flex-direction:column;gap:.6rem;max-width:42em}
.about h2{font-size:1.45rem;color:var(--wine)}
.portrait{margin:0;width:11rem;background:var(--paper);padding:.55rem .55rem .4rem;border:1px solid var(--line);box-shadow:0 0 0 4px var(--sheet),0 0 0 5px var(--line),0 .6rem 1.2rem var(--shadow);transform:rotate(-1deg)}
.portrait img{display:block;width:100%;height:auto;aspect-ratio:3/4;object-fit:cover}
.portrait figcaption{font:italic .9rem/1.3 var(--text);text-align:center;color:var(--ink2);margin-top:.4rem}
.brand-note{font-style:italic;color:var(--ink2);font-size:.98rem;border-left:2px solid var(--gold);padding-left:.8rem}
.fine{font-size:.88rem;color:var(--ink2)}
.copy{font-weight:600;font-size:.95rem}

/* ---------- màn hình vừa và nhỏ ---------- */
@media (max-width:960px){
  .hero-in{grid-template-columns:1fr;gap:2rem}
  .plate{max-width:34rem}
  .how-list{grid-template-columns:1fr}
  .split{grid-template-columns:1fr;grid-template-rows:var(--top) .9rem minmax(0,1fr)}
  .pane-quiz{border-left:0;border-top:1px solid var(--line)}
  .split-bar{cursor:row-resize}
  .split-bar::before{top:50%;bottom:auto;left:0;right:0;border-left:0;border-top:3px double var(--line);transform:translateY(-50%)}
  .split-bar span{width:2.6rem;height:.55rem}
}
@media (max-width:640px){
  .site-nav{display:none}
  .fs{margin-left:auto}
  .lb span{display:none}
  .lb{padding:.3rem .45rem}
  .hero{padding-block:2rem 1.6rem}
  .btn.big{width:100%}
  .about{grid-template-columns:1fr;justify-items:start}
  .portrait{width:9rem}
  .row{grid-template-columns:2rem minmax(0,1fr);row-gap:.3rem}
  .row .st{grid-column:2}
  .app{min-height:20rem;font-size:.72rem}
  .sb{flex-basis:28%;padding:.5rem .25rem}
  .sb .sec,.sb .rc{display:none}
  .ib .mdl{display:none}
  .m{max-width:94%}
  .pane{padding:1.1rem 1rem 2rem}
  .lesson-bar .bar{display:none}
}
@media (prefers-reduced-motion:reduce){
  html{scroll-behavior:auto}
  *,*::before,*::after{animation:none!important;transition:none!important}
}
@media (max-width:640px){
  body.in-lesson .brand span:last-child{display:none}
  .fs-b{min-width:2.15rem}
}

/* ---------- góp ý ẩn danh ---------- */
.fbk{margin-top:2.2rem;padding:1.1rem 1.2rem;border:1px solid var(--line);background:var(--paper);display:flex;flex-direction:column;gap:.7rem}
.fbk h3{font-size:1.08rem}
.fb-btns{display:flex;gap:.6rem;flex-wrap:wrap}
.fbb{font:600 .98rem/1.2 var(--text);min-height:2.75rem;padding:.6rem 1.1rem;border-radius:3px;border:1px solid var(--line);background:var(--sheet);color:var(--ink);cursor:pointer}
.fbb.up::before{content:"✓  ";color:var(--wine)}
.fbb.down::before{content:"?  ";color:var(--gold);font-family:var(--display)}
.fbb:hover:not(:disabled){border-color:var(--wine)}
.fbb:disabled{cursor:default;opacity:.6}
.fbb.on{opacity:1;border-color:var(--wine);box-shadow:inset 0 0 0 1px var(--wine);background:color-mix(in srgb,var(--wine) 8%,var(--sheet))}
.fb-more{display:flex;flex-direction:column;gap:.5rem;align-items:flex-start}
.fbk textarea,.fb-form textarea{width:100%;font:400 1rem/1.55 var(--text);color:var(--ink);background:var(--sheet);border:1px solid var(--line);border-radius:3px;padding:.65rem .8rem;resize:vertical;min-height:5.5rem}
.fbk textarea:focus,.fb-form textarea:focus{outline:2px solid var(--gold);outline-offset:1px;border-color:var(--gold)}
.fb-status{font-size:.95rem;min-height:1.3em}
.fb-status:empty{display:none}
.fb-status.good{color:var(--wine);font-style:italic}
.fb-status.bad{color:var(--wine);font-weight:600}
.fb-done{color:var(--ink2);font-style:italic}
.fb-course{display:flex;flex-direction:column;gap:.6rem;max-width:42em;padding-top:1.2rem;border-top:1px solid var(--line)}
.fb-course h2{font-size:1.3rem;color:var(--wine)}
.fb-form{display:flex;flex-direction:column;gap:.7rem;margin-top:.2rem}
.fb-cats{border:0;margin:0;padding:0;display:flex;flex-wrap:wrap;gap:.5rem}
.fb-cats legend{font:700 .98rem/1.4 var(--display);margin-bottom:.4rem;padding:0}
.chip{display:inline-flex;align-items:center;gap:.45rem;padding:.45rem .85rem;border:1px solid var(--line);border-radius:999px;background:var(--paper);cursor:pointer;font-size:.97rem}
.chip input{accent-color:var(--wine);margin:0}
.chip:has(input:checked){border-color:var(--wine);background:color-mix(in srgb,var(--wine) 8%,var(--paper))}
.chip:has(input:focus-visible){outline:2px solid var(--gold);outline-offset:2px}
.fb-count{font-size:.85rem;color:var(--ink2);text-align:right;margin-top:-.4rem}
.fb-actions{display:flex;gap:.7rem;flex-wrap:wrap}
.hp{position:absolute;left:-9999px;width:1px;height:1px;overflow:hidden}

/* ---------- nhà tài trợ ---------- */
.sp-label{font:600 .78rem/1.2 var(--ui);letter-spacing:.14em;text-transform:uppercase;color:var(--gold)}
.sp-home{padding-block:0 2.2rem;display:flex;flex-direction:column;gap:.8rem}
.sp-list{display:grid;grid-template-columns:repeat(auto-fill,minmax(min(100%,17rem),1fr));gap:1rem}
.sp-card{display:flex;align-items:center;gap:1rem;padding:.9rem 1.1rem;border:1px solid var(--line);background:var(--sheet);color:var(--ink);text-decoration:none;border-radius:3px;min-width:0}
.sp-card:hover{border-color:var(--gold);box-shadow:0 2px 10px var(--shadow)}
.sp-card img{flex:none;max-height:3rem;max-width:6.5rem;width:auto;height:auto;object-fit:contain}
.sp-txt{display:flex;flex-direction:column;gap:.15rem;min-width:0}
.sp-txt b{font-family:var(--display);font-size:1.02rem;color:var(--wine)}
.sp-txt span{font-size:.94rem;color:var(--ink2);line-height:1.45}
.sp-lesson{margin-top:1.6rem;max-width:40em;display:flex;flex-direction:column;gap:.5rem}
.sp-foot{display:flex;flex-direction:column;gap:.7rem}
.sp-foot h2{font:600 .78rem/1.2 var(--ui);letter-spacing:.14em;text-transform:uppercase;color:var(--gold)}
.sp-logos{display:flex;flex-wrap:wrap;gap:.8rem 1.4rem;align-items:center}
.sp-logo{display:inline-flex;align-items:center;gap:.6rem;color:var(--ink);text-decoration:none;opacity:.9}
.sp-logo:hover{opacity:1}
.sp-logo img{max-height:2.4rem;max-width:7rem;width:auto;height:auto;object-fit:contain}
.sp-logo .sp-txt b{font-size:.95rem;color:var(--ink2)}
.sp-logo img + .sp-txt{position:absolute;width:1px;height:1px;overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap}
.fbb.up::before,.fbb.down::before{font-family:var(--ui);font-weight:700}
.sp-foot{padding-top:1.2rem;border-top:1px solid var(--line);max-width:42em}
/* hướng dẫn khi không nghe thấy giọng đọc */
.vhelp{margin-top:.7rem;font-family:var(--text);font-size:.95rem;color:var(--ink2)}
.vhelp summary{cursor:pointer;color:var(--wine);font-weight:600;width:max-content;max-width:100%}
.vhelp p{margin-top:.45rem;line-height:1.55}
.vhelp.warn{padding:.7rem .9rem;border-left:3px solid var(--gold);background:var(--hl)}
.vhelp .vwarn{color:var(--ink);font-weight:600}