/* Local system typography and reusable surfaces. No external assets. */
:root{
  color-scheme:light;
  --ink:#24272d;--muted:#616875;--blue:#2469cc;--blue-hover:#1958b2;
  --blue-soft:#edf3fd;--line:#e0e3e9;--paper:#fff;--background:#f5f6f8;
  --error:#a12d36;--focus:#296fd0;--radius:20px;
  font:17px/1.65 system-ui,-apple-system,"Segoe UI","Microsoft YaHei",sans-serif;
}
*{box-sizing:border-box}
body{margin:0;background:var(--background);color:var(--ink);overflow-wrap:anywhere;-webkit-font-smoothing:antialiased}
button,input,textarea,select{font:inherit}
button,a,input,textarea,select{touch-action:manipulation}
button{min-height:48px;max-width:100%;padding:10px 18px;border:1px solid var(--line);border-radius:11px;background:var(--paper);color:var(--ink);font-weight:600;line-height:1.5;cursor:pointer;overflow-wrap:anywhere;transition:background-color 140ms ease,border-color 140ms ease,box-shadow 140ms ease}
button:hover:not(:disabled){background:#f0f2f6;border-color:#c7ccd5}
button:active:not(:disabled){background:#e8ebf1}
button:disabled{opacity:.48;cursor:default}
button.primary{background:var(--blue);border-color:var(--blue);color:#fff;box-shadow:0 2px 5px #245db51c}
button.primary:hover:not(:disabled){background:var(--blue-hover);border-color:var(--blue-hover)}
button.quiet{background:transparent;border-color:transparent;color:var(--muted);padding-inline:12px}
button.quiet:hover:not(:disabled){color:var(--ink);background:#e9ecf2;border-color:transparent}
a{color:var(--blue)}
:focus-visible{outline:3px solid var(--focus);outline-offset:4px}
h1:focus,main:focus{outline:none}
h1{font-size:1.65rem;line-height:1.35;font-weight:700;letter-spacing:-.035em;margin:0 0 12px}
h2{font-size:1.18rem;line-height:1.45;letter-spacing:-.015em;margin:0 0 16px}
h3{font-size:1.04rem;line-height:1.5;margin:0 0 10px}
p{margin:0 0 16px}p:last-child{margin-bottom:0}
[hidden]{display:none!important}
.site-header{max-width:1060px;margin:auto;padding:24px 30px 18px;display:flex;align-items:center;justify-content:space-between;gap:12px}
.brand{font-size:1.06rem;font-weight:730;letter-spacing:-.035em;line-height:1.35}
.header-actions{display:flex;gap:4px;flex-wrap:wrap;justify-content:flex-end}
.header-actions button{font-size:.94rem}
.skip-link{position:absolute;top:-120px;left:12px;padding:12px 16px;z-index:30;background:var(--paper);border-radius:9px}
.skip-link:focus{top:8px}
main{max-width:1000px;margin:14px auto 64px;padding:0 30px;min-width:0}
.notice,.network-state{max-width:940px;margin:0 auto 14px;padding:13px 18px;border-radius:12px;background:#e9f2ec;color:#255039;border:1px solid #d0e3d6}
.notice.error,.network-state{background:#fff0f0;color:var(--error);border-color:#edc4c8}
#busy-indicator{max-width:940px;margin:0 auto 12px;padding:0 18px;color:var(--muted);font-size:.95rem}
.loading{padding:32px 0;color:var(--muted)}
.paper{min-width:0;background:var(--paper);border:1px solid var(--line);border-radius:var(--radius);padding:34px;box-shadow:0 2px 3px #1e273405,0 12px 35px #1e273408}
.login-paper{max-width:470px;margin:48px auto;padding:38px}
.login-paper form>.muted{margin-top:12px}
.eyebrow{font-size:.9rem;color:var(--muted);font-weight:550;margin-bottom:10px}
.muted{color:var(--muted)}
.page-top{display:flex;align-items:flex-start;justify-content:space-between;gap:16px;margin-bottom:26px}
.page-top>div{min-width:0}
.actions{display:flex;align-items:center;flex-wrap:wrap;gap:10px;margin-top:22px}
.actions>*{max-width:100%}
.full-width{width:100%}
.form-field{display:block;margin:22px 0}
.field-label{display:block;font-weight:600;margin-bottom:9px}
input[type=text],input[type=password],textarea,select{width:100%;min-width:0;min-height:50px;padding:12px 14px;border:1px solid #bac1cc;border-radius:10px;background:#fff;color:var(--ink)}
select{white-space:normal}
textarea{min-height:120px;resize:vertical}
.form-field textarea{min-height:150px}
input[type=checkbox]{width:22px;height:22px;flex:0 0 22px;accent-color:var(--blue)}
.check-label{display:flex;align-items:center;gap:12px;min-height:48px;cursor:pointer}
.check-label span{min-width:0}
.login-note{margin-top:24px;padding-top:20px;border-top:1px solid var(--line);color:var(--muted)}
.stats{display:flex;gap:36px;flex-wrap:wrap;padding:24px 0;border-block:1px solid var(--line);margin:26px 0}
.stat strong{display:block;font-size:1.9rem;line-height:1.15;font-weight:650;letter-spacing:-.04em;font-variant-numeric:tabular-nums;margin-bottom:7px}
.stat span{color:var(--muted)}
.task-list{list-style:none;padding:0;margin:22px 0 0}
.task-list li{display:flex;align-items:center;gap:16px;padding:18px 0;border-top:1px solid var(--line)}
.task-list li>div{flex:1;min-width:0}
.task-number{color:var(--muted);font-variant-numeric:tabular-nums}
.tag{display:inline-block;font-size:.88rem;line-height:1.6;color:#436084;background:#eef2f7;border-radius:5px;padding:2px 9px;margin-right:9px}
.card-front,.math-text{min-width:0;max-width:100%;white-space:pre-wrap;font-size:1.13rem;line-height:1.9;overflow-wrap:anywhere}
.katex{font-size:1.13em}
.katex-display{max-width:100%;overflow-x:auto;overflow-y:hidden;padding:9px 2px;margin:18px 0!important}
.katex-display>.katex{white-space:nowrap}
.math-text>.katex,.card-front>.katex{display:inline-block;max-width:100%;overflow-x:auto;overflow-y:hidden;vertical-align:middle;padding-block:3px}
.formula-scroll-hint{font-size:1rem;line-height:1.6;color:var(--muted);margin:12px 0}
[data-control="formula-scroll"]{overscroll-behavior-x:contain;-webkit-overflow-scrolling:touch;touch-action:pan-x pan-y}
[data-control="formula-scroll"]:focus-visible{outline:3px solid var(--focus);outline-offset:2px}
/* The current review card is the primary surface. */
.study-session{width:100%;max-width:760px;margin:0 auto;min-width:0;perspective:1100px}
.study-topbar{display:flex;align-items:center;justify-content:space-between;gap:8px 14px;flex-wrap:wrap;margin:0 2px 18px;color:var(--muted)}
.study-topbar>p{margin:0;flex:1;text-align:center;font-variant-numeric:tabular-nums}
.study-topbar button{border-color:transparent;background:transparent;color:var(--muted);padding-inline:10px}
.study-topbar button:hover:not(:disabled){background:#e9ecf2;color:var(--ink)}
.study-card{position:relative;min-width:0;min-height:340px;padding:36px 40px 40px;border:1px solid #dadee6;border-radius:24px;background:#fff;box-shadow:0 1px 2px #1923370a,0 15px 35px #1923370c,0 35px 65px #19233705;transform-origin:50% 45%;backface-visibility:hidden}
.study-card[data-side=back]{border-color:#cfd9e8}
.card-face-label{font-size:.88rem;font-weight:600;letter-spacing:.03em;color:#657187;margin-bottom:22px}
.study-card h1{font-size:1.32rem;line-height:1.5;letter-spacing:-.02em;margin-bottom:22px}
.study-card .card-front{font-size:1.2rem;line-height:1.9}
.study-card .answer-box{margin-top:30px;padding-top:26px}
.study-card .answer-box h2{color:#52647e;font-size:1rem;font-weight:600}
.answer-box{margin-top:30px;padding-top:25px;border-top:1px solid var(--line)}
.study-heading{margin-bottom:24px}.study-heading h1{font-size:1.4rem}
.study-lead{color:var(--muted);margin-bottom:22px}
.review-dock{position:sticky;bottom:14px;z-index:5;margin:20px auto 0;padding:12px;background:rgba(255,255,255,.97);border:1px solid #dfe3ea;border-radius:18px;box-shadow:0 5px 18px #202d4210;max-width:100%;min-width:0}
.reveal-actions{display:flex;justify-content:center;gap:10px}
.reveal-actions button{min-width:min(260px,100%);min-height:54px}
.review-dock .actions{margin-top:0}
.rating-grid{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:9px;min-width:0}
.rating-grid button{min-width:0;min-height:57px;padding:12px 10px;text-align:center;font-weight:650;border-radius:11px}
.rating-grid button span{display:block;font-size:.88rem;font-weight:400;margin-top:4px}
.rating-grid .rating-interval{font-variant-numeric:tabular-nums;line-height:1.4}
.waiting-paper{max-width:760px;margin-inline:auto}
.waiting-summary{padding:24px 0}
.waiting-clock{font-size:2.25rem;font-weight:600;font-variant-numeric:tabular-nums;letter-spacing:-.03em;color:var(--ink);line-height:1.3}
.next-review-time{font-variant-numeric:tabular-nums}
.rating-grid .rating-again{color:#aa3541;background:#fff0f1;border-color:#f0cbd0}
.rating-grid .rating-hard{color:#94601b;background:#fff5e5;border-color:#ecd8b7}
.rating-grid .rating-good{color:#255eac;background:#edf4ff;border-color:#cadcf6}
.rating-grid .rating-easy{color:#287248;background:#ecf7ef;border-color:#c8e4d0}
.rating-grid .rating-again:hover:not(:disabled){background:#fde0e4;border-color:#deaab3}
.rating-grid .rating-hard:hover:not(:disabled){background:#ffecd0;border-color:#dac296}
.rating-grid .rating-good:hover:not(:disabled){background:#dceaff;border-color:#accaf0}
.rating-grid .rating-easy:hover:not(:disabled){background:#d8efdf;border-color:#aad3b7}
.study-extras{margin:22px 6px 0;color:var(--muted)}
.study-extras .feedback{margin-top:12px;padding-top:8px}
.study-extras .feedback summary{font-weight:500;color:var(--muted)}
.study-extras .feedback[open]{padding-top:16px;color:var(--ink)}
.study-extras .feedback[open] summary{color:var(--ink)}
.feedback{margin-top:30px;padding-top:20px;border-top:1px solid var(--line)}
.feedback summary{min-height:48px;cursor:pointer;display:list-item;padding:10px 0;color:#415a7d;font-weight:550}
.feedback textarea{margin:10px 0}.feedback-note{color:var(--muted);margin-top:12px}
/* Teacher workspace and low-frequency forms. */
.toolbar{display:flex;flex-wrap:wrap;gap:4px;margin-bottom:28px;padding:5px;border-radius:14px;background:#eef0f4}
.toolbar button{border-color:transparent;background:transparent;color:var(--muted);flex:1;min-width:0;padding-inline:14px}
.toolbar button[aria-current=page]{background:#fff;border-color:#e1e4ea;color:#255fae;box-shadow:0 2px 4px #202d420a}
.section{margin-top:32px}
.list-row{display:flex;align-items:center;justify-content:space-between;gap:14px;padding:18px 0;border-bottom:1px solid var(--line)}
.list-row>div{min-width:0}.row-detail{margin-top:6px;color:var(--muted)}
.selection-box{border:0;border-top:1px solid var(--line);padding:20px 0;margin:28px 0 0;min-width:0}
.selection-box legend{font-weight:600;padding:0 8px 0 0}
.student-options{display:flex;gap:10px 25px;flex-wrap:wrap}
.feedback-item{padding:24px 0;border-bottom:1px solid var(--line)}
.feedback-item .math-text{margin-top:10px;font-size:1rem}.feedback-item h3{margin-bottom:6px}.feedback-item .actions{margin-top:12px}
.help-form{margin-block:16px 24px}.message-text{white-space:pre-wrap}
.review-list{list-style:none;padding:0}.review-list li{padding:18px 0;border-bottom:1px solid var(--line)}.review-list button{margin-top:12px}
.table-scroll{max-width:100%;overflow-x:auto}
table{border-collapse:collapse;width:100%;text-align:left}
th,td{padding:15px 12px;border-bottom:1px solid var(--line);white-space:nowrap}
th:first-child,td:first-child{padding-left:0}th{font-weight:600;color:var(--muted)}
.empty-state{padding:26px 0}.success-mark{font-size:2rem;color:#367356;margin-bottom:12px}
.source-note{margin-top:22px;padding-top:18px;border-top:1px solid var(--line);color:var(--muted)}
.action-error{color:var(--error);margin-top:14px}
.count-chip{background:var(--blue-soft);padding:4px 11px;border-radius:7px;white-space:nowrap;color:#355d92}
.render-error{margin-block:24px;padding:20px;border:1px solid #edc4c8;background:#fff1f2;color:#922d39;border-radius:12px}
.render-failed{border-left:3px solid #b5616c;padding-left:12px}
.revision-notice,.corrections{padding:18px;background:#fff8e9;border:1px solid #e7d8b8;border-radius:12px;margin-block:20px}
dialog{border:1px solid #dce0e7;border-radius:22px;padding:30px;max-width:560px;width:calc(100% - 32px);max-height:85dvh;overflow:auto;color:var(--ink);background:#fff;box-shadow:0 20px 80px #111d3533}
dialog::backdrop{background:#16213666}
dialog .actions{justify-content:flex-end}dialog ul{padding-inline-start:24px}
.large-text{font-size:20px}.huge-text{font-size:34px}
/* One short entry per card, and a restrained turn into the answer. */
.card-enter{animation:card-enter 240ms cubic-bezier(.2,.7,.25,1) both}
.card-reveal{animation:card-reveal 260ms cubic-bezier(.2,.7,.25,1) both}
@keyframes card-enter{from{opacity:.3;transform:translateY(12px) scale(.988)}to{opacity:1;transform:translateY(0) scale(1)}}
@keyframes card-reveal{from{opacity:.35;transform:rotateY(-9deg) translateY(3px)}to{opacity:1;transform:rotateY(0) translateY(0)}}
@media(max-width:600px){
  .site-header{padding:16px 18px 10px}.header-actions{gap:0}.header-actions button{padding-inline:10px}
  main{padding:0 16px;margin-top:12px}.paper{padding:25px 21px;border-radius:18px}.login-paper{margin-top:30px;padding:30px 24px}
  .notice,.network-state{margin-inline:16px}.page-top{gap:8px;margin-bottom:22px}.page-top h1{font-size:1.45rem}
  .stats{gap:28px}.card-front,.math-text{font-size:1.08rem}
  .study-topbar{gap:6px;margin-bottom:12px}.study-topbar button{padding-inline:8px;font-size:.94rem}
  .study-card{min-height:300px;padding:28px 24px 32px;border-radius:21px;box-shadow:0 1px 2px #1923370a,0 12px 26px #1923370d}
  .study-card .card-front{font-size:1.13rem}.study-card h1{font-size:1.2rem}.card-face-label{margin-bottom:18px}
  .review-dock{margin-top:17px;padding:10px;bottom:10px;border-radius:16px}.rating-grid{gap:7px}.rating-grid button{padding:12px 5px;min-height:54px}
  .study-extras{margin-top:20px}.list-row{align-items:flex-start;flex-wrap:wrap}.list-row>.check-label{flex:1;min-width:150px}
  .toolbar button{padding-inline:10px}.task-list li{gap:10px}.actions{align-items:stretch}.actions button{flex-grow:1}.student-options{display:block}
}
@media(max-width:360px){
  .site-header{padding-inline:14px}.brand{font-size:1rem}.header-actions button{padding-inline:8px}main{padding-inline:12px}
  .study-card{padding-inline:20px}.paper{padding-inline:18px}.page-top{flex-wrap:wrap}
  .study-topbar{flex-wrap:wrap}.study-topbar>p{order:3;flex-basis:100%;text-align:left;margin:4px 8px}
}
.large-text .site-header,.huge-text .site-header{flex-wrap:wrap}
.large-text .header-actions,.huge-text .header-actions{margin-left:auto}
.huge-text .page-top{flex-wrap:wrap}.huge-text .stats{gap:20px}.huge-text .paper{padding:24px 18px}
.huge-text .task-list li{align-items:flex-start}.huge-text .task-number{font-size:.8rem}
.huge-text .study-topbar{flex-wrap:wrap}.huge-text .study-topbar>*{max-width:100%}
.huge-text .study-topbar>p{flex-basis:100%;text-align:left;order:3}
.huge-text .study-card{padding:28px 19px;min-height:300px}.huge-text .study-card h1{font-size:1.12rem}
.huge-text .review-dock{position:static;padding:10px}.huge-text .rating-grid{grid-template-columns:repeat(2,minmax(0,1fr));gap:8px}
.huge-text .rating-grid button{padding:12px 7px}.huge-text .toolbar{flex-direction:column}.huge-text .study-extras{margin-inline:0}
@media(prefers-reduced-motion:reduce){*,*::before,*::after{animation:none!important;transition:none!important;scroll-behavior:auto!important}.card-enter,.card-reveal{transform:none!important;opacity:1!important}}
@media(forced-colors:active){button,.paper,.study-card,.review-dock,.tag,.render-error,.corrections{border:1px solid CanvasText;box-shadow:none}button.primary,.toolbar button[aria-current=page]{border:2px solid ButtonText}.rating-grid button{color:ButtonText;background:ButtonFace}}

.login-switch{margin-top:14px}
.queue-toggle{margin-top:16px}