/* ============================================================
   数学ラボ — app.css
   ライト / ダーク両対応・タブレット最適化
   ============================================================ */
:root{
  --bg:#f5f6fb;
  --bg-soft:#eceefa;
  --surface:#ffffff;
  --surface-2:#f8f9fe;
  --border:#dfe3f0;
  --border-strong:#c9cfe4;
  --text:#1a1f36;
  --text-soft:#4a5372;
  --muted:#767f9c;
  --accent:#3b4fd8;
  --accent-2:#6b46e0;
  --accent-soft:#e8ebfd;
  --ok:#15803d;
  --ok-soft:#e5f6ec;
  --warn:#b45309;
  --warn-soft:#fdf1e0;
  --ng:#b91c1c;
  --ng-soft:#fde8e8;
  --radius:14px;
  --radius-sm:9px;
  --shadow:0 1px 2px rgba(20,26,60,.06),0 8px 24px -12px rgba(20,26,60,.18);
  --shadow-lg:0 12px 40px -16px rgba(20,26,60,.32);
  --mono:"SFMono-Regular",Consolas,"Liberation Mono",Menlo,monospace;
  --serif:"Hiragino Mincho ProN","Yu Mincho",'Noto Serif JP',serif;
  --sans:-apple-system,BlinkMacSystemFont,"Hiragino Sans","Hiragino Kaku Gothic ProN","Noto Sans JP",Roboto,"Segoe UI",sans-serif;
  --header-h:58px;
}
body[data-theme="dark"]{
  --bg:#0f1120;
  --bg-soft:#161a2e;
  --surface:#191d33;
  --surface-2:#1f2440;
  --border:#2b3152;
  --border-strong:#3a4166;
  --text:#e9ecf8;
  --text-soft:#c0c6e0;
  --muted:#8d96b8;
  --accent:#8a97ff;
  --accent-2:#b18cff;
  --accent-soft:#232a4d;
  --ok:#6ee7a0;
  --ok-soft:#12301f;
  --warn:#f5c07a;
  --warn-soft:#33240f;
  --ng:#ff9a9a;
  --ng-soft:#3a1618;
  --shadow:0 1px 2px rgba(0,0,0,.4),0 10px 30px -14px rgba(0,0,0,.7);
  --shadow-lg:0 16px 48px -18px rgba(0,0,0,.8);
}
*,*::before,*::after{box-sizing:border-box}
html{-webkit-text-size-adjust:100%}
body{
  margin:0;background:var(--bg);color:var(--text);
  font-family:var(--sans);font-size:15.5px;line-height:1.75;
  -webkit-font-smoothing:antialiased;overscroll-behavior-y:none;
}
a{color:var(--accent);text-decoration:none}
a:hover{text-decoration:underline}
h1,h2,h3,h4{line-height:1.35;margin:0 0 .5em;font-weight:700;letter-spacing:.01em}
h1{font-size:1.7rem}h2{font-size:1.32rem}h3{font-size:1.1rem}h4{font-size:.98rem}
p{margin:0 0 .8em}
small{font-size:.8rem}
.muted{color:var(--muted)}
.mono{font-family:var(--mono);font-size:.9em}
hr{border:0;border-top:1px solid var(--border);margin:1.2rem 0}
.skip-link{position:absolute;left:-9999px;top:0;background:var(--accent);color:#fff;padding:.6rem 1rem;z-index:9999;border-radius:0 0 8px 0}
.skip-link:focus{left:0}

/* ---------- header ---------- */
.site-header{
  position:sticky;top:0;z-index:60;background:color-mix(in srgb,var(--surface) 88%,transparent);
  backdrop-filter:saturate(180%) blur(12px);border-bottom:1px solid var(--border);
}
.header-inner{
  max-width:1240px;margin:0 auto;padding:.45rem 1rem;
  display:flex;align-items:center;gap:.9rem;min-height:var(--header-h);
}
.brand{display:flex;align-items:center;gap:.6rem;color:var(--text);text-decoration:none;flex:0 0 auto}
.brand:hover{text-decoration:none}
.brand-mark{
  width:34px;height:34px;border-radius:10px;display:grid;place-items:center;
  background:linear-gradient(135deg,var(--accent),var(--accent-2));color:#fff;
  font-family:var(--serif);font-size:1.25rem;font-weight:700;box-shadow:var(--shadow)
}
.brand-text{display:flex;flex-direction:column;line-height:1.15}
.brand-text strong{font-size:1rem;letter-spacing:.03em}
.brand-text small{color:var(--muted);font-size:.68rem;letter-spacing:.02em}
.main-nav{display:flex;gap:.1rem;overflow-x:auto;flex:1 1 auto;scrollbar-width:none}
.main-nav::-webkit-scrollbar{display:none}
.main-nav a{
  padding:.4rem .62rem;border-radius:999px;color:var(--text-soft);font-size:.87rem;
  white-space:nowrap;font-weight:600
}
.main-nav a:hover{background:var(--bg-soft);text-decoration:none;color:var(--text)}
.main-nav a.active{background:var(--accent-soft);color:var(--accent)}
.header-tools{display:flex;gap:.35rem;flex:0 0 auto}
.icon-btn{
  border:1px solid var(--border);background:var(--surface);color:var(--text-soft);
  width:34px;height:34px;border-radius:10px;cursor:pointer;font-size:.95rem;
  display:grid;place-items:center;transition:.15s
}
.icon-btn:hover{background:var(--bg-soft);color:var(--text);border-color:var(--border-strong)}

/* ---------- layout ---------- */
.app-main{max-width:1240px;margin:0 auto;padding:1.1rem 1rem 3rem;min-height:60vh}
.app-main:focus{outline:none}
.site-footer{border-top:1px solid var(--border);background:var(--surface);padding:1.2rem 1rem 2rem}
.footer-inner{max-width:1240px;margin:0 auto;font-size:.82rem;color:var(--text-soft)}
.footer-inner p{margin:.2rem 0}
.stack{display:flex;flex-direction:column;gap:1rem}
.row{display:flex;gap:.6rem;flex-wrap:wrap;align-items:center}
.row.tight{gap:.35rem}
.spread{display:flex;justify-content:space-between;align-items:center;gap:1rem;flex-wrap:wrap}
.grid{display:grid;gap:1rem}
.grid.cols-2{grid-template-columns:repeat(auto-fit,minmax(280px,1fr))}
.grid.cols-3{grid-template-columns:repeat(auto-fit,minmax(230px,1fr))}
.grid.cols-4{grid-template-columns:repeat(auto-fit,minmax(180px,1fr))}

/* ---------- cards ---------- */
.card{
  background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);
  padding:1.05rem 1.1rem;box-shadow:var(--shadow)
}
.card.flat{box-shadow:none}
.card.pad-lg{padding:1.4rem}
.card-title{display:flex;align-items:center;gap:.5rem;margin-bottom:.6rem;font-weight:700}
.card-title .ic{font-size:1.05rem}
.card h3{margin-bottom:.4rem}
.hero{
  background:linear-gradient(135deg,color-mix(in srgb,var(--accent) 92%,#000 8%),var(--accent-2));
  color:#fff;border:0
}
.hero h1{color:#fff;margin-bottom:.35rem}
.hero p{color:#e7e9ff}
.hero .stat{background:rgba(255,255,255,.16);border:1px solid rgba(255,255,255,.22);border-radius:12px;padding:.55rem .8rem;min-width:98px}
.hero .stat b{display:block;font-size:1.35rem;line-height:1.2}
.hero .stat span{font-size:.74rem;opacity:.9}

/* ---------- buttons ---------- */
.btn{
  display:inline-flex;align-items:center;justify-content:center;gap:.42rem;
  border:1px solid var(--border-strong);background:var(--surface);color:var(--text);
  padding:.5rem .9rem;border-radius:10px;font:inherit;font-size:.9rem;font-weight:600;
  cursor:pointer;transition:.15s;text-decoration:none;line-height:1.3
}
.btn:hover{background:var(--bg-soft);text-decoration:none}
.btn:active{transform:translateY(1px)}
.btn:disabled{opacity:.5;cursor:not-allowed}
.btn.primary{background:var(--accent);border-color:var(--accent);color:#fff}
.btn.primary:hover{filter:brightness(1.06)}
.btn.ghost{background:transparent;border-color:transparent;color:var(--text-soft)}
.btn.ghost:hover{background:var(--bg-soft);color:var(--text)}
.btn.sm{padding:.3rem .6rem;font-size:.8rem;border-radius:8px}
.btn.lg{padding:.68rem 1.15rem;font-size:.98rem}
.btn.ok{background:var(--ok-soft);border-color:color-mix(in srgb,var(--ok) 40%,var(--border));color:var(--ok)}
.btn.danger{color:var(--ng);border-color:color-mix(in srgb,var(--ng) 40%,var(--border))}
.btn.block{width:100%}
.btn-group{display:flex;flex-wrap:wrap;gap:.35rem}

/* ---------- forms ---------- */
label.field{display:block;margin-bottom:.7rem}
label.field > span.lbl{display:block;font-size:.8rem;font-weight:700;color:var(--text-soft);margin-bottom:.3rem}
input[type=text],input[type=search],input[type=number],input[type=password],select,textarea{
  width:100%;font:inherit;font-size:.92rem;padding:.5rem .7rem;border-radius:9px;
  border:1px solid var(--border-strong);background:var(--surface);color:var(--text)
}
input:focus,select:focus,textarea:focus{outline:2px solid color-mix(in srgb,var(--accent) 45%,transparent);outline-offset:1px;border-color:var(--accent)}
textarea{resize:vertical;min-height:80px}
input[type=range]{width:100%;accent-color:var(--accent)}
.inline-input{font-family:var(--mono);font-size:1rem;letter-spacing:.02em}
.check{display:flex;gap:.5rem;align-items:flex-start;font-size:.9rem;margin-bottom:.35rem}
.check input{margin-top:.3rem;accent-color:var(--accent)}
fieldset{border:1px solid var(--border);border-radius:var(--radius-sm);padding:.8rem;margin:0 0 .8rem}
legend{font-size:.8rem;font-weight:700;color:var(--text-soft);padding:0 .35rem}

/* ---------- badges ---------- */
.badge{
  display:inline-flex;align-items:center;gap:.25rem;font-size:.72rem;font-weight:700;
  padding:.12rem .5rem;border-radius:999px;border:1px solid var(--border);
  background:var(--surface-2);color:var(--text-soft);white-space:nowrap
}
.badge.accent{background:var(--accent-soft);color:var(--accent);border-color:transparent}
.badge.ok{background:var(--ok-soft);color:var(--ok);border-color:transparent}
.badge.warn{background:var(--warn-soft);color:var(--warn);border-color:transparent}
.badge.ng{background:var(--ng-soft);color:var(--ng);border-color:transparent}
.lvl{display:inline-flex;gap:1px;letter-spacing:0}
.lvl i{width:6px;height:12px;border-radius:2px;background:var(--border-strong);display:inline-block}
.lvl i.on{background:var(--accent)}
.lvl.auto i.on:nth-child(4),.lvl.auto i.on:nth-child(5){background:var(--warn)}

/* ---------- lists / tables ---------- */
ul.clean,ol.clean{margin:.2rem 0 .8rem;padding-left:1.15rem}
ul.clean li,ol.clean li{margin-bottom:.28rem}
ul.dash{list-style:none;padding-left:0}
ul.dash li{padding-left:1.1rem;position:relative;margin-bottom:.3rem}
ul.dash li::before{content:"—";position:absolute;left:0;color:var(--muted)}
table.tbl{width:100%;border-collapse:collapse;font-size:.87rem}
table.tbl th,table.tbl td{text-align:left;padding:.45rem .5rem;border-bottom:1px solid var(--border)}
table.tbl th{font-size:.76rem;color:var(--text-soft);font-weight:700;background:var(--surface-2)}
table.tbl tr:last-child td{border-bottom:0}

/* ---------- math ---------- */
.katex{font-size:1.045em}
.math-block{overflow-x:auto;overflow-y:hidden;padding:.35rem 0;text-align:center}
.math-block .katex-display{margin:.35rem 0}
mjx-container{overflow-x:auto;overflow-y:hidden;max-width:100%}
.tex-fallback{font-family:var(--mono);background:var(--surface-2);padding:.1rem .3rem;border-radius:4px}

/* ---------- problem / work views ---------- */
.work-layout{display:grid;grid-template-columns:minmax(0,1fr) 330px;gap:1rem;align-items:start}
@media(max-width:1000px){.work-layout{grid-template-columns:1fr}}
.q-stem{font-size:1.02rem;line-height:1.9}
.q-meta{display:flex;gap:.4rem;flex-wrap:wrap;margin-bottom:.7rem}
.tabs{display:flex;gap:.2rem;border-bottom:1px solid var(--border);margin:1rem 0 .9rem;overflow-x:auto;scrollbar-width:none}
.tabs::-webkit-scrollbar{display:none}
.tabs button{
  border:0;background:transparent;font:inherit;font-size:.88rem;font-weight:700;color:var(--muted);
  padding:.5rem .8rem;border-bottom:2px solid transparent;cursor:pointer;white-space:nowrap
}
.tabs button.active{color:var(--accent);border-bottom-color:var(--accent)}
.tabs button:hover{color:var(--text)}
.mode-chips{display:flex;gap:.35rem;flex-wrap:wrap;margin:.2rem 0 .9rem}
.chip{
  border:1px solid var(--border-strong);background:var(--surface);border-radius:999px;
  padding:.25rem .7rem;font-size:.8rem;font-weight:700;color:var(--text-soft);cursor:pointer
}
.chip.active{background:var(--accent);border-color:var(--accent);color:#fff}
.answer-row{display:flex;gap:.5rem;align-items:stretch;flex-wrap:wrap}
.answer-row .inline-input{flex:1 1 220px}
.verdict{margin-top:.7rem;border-radius:10px;padding:.6rem .8rem;font-size:.9rem;border:1px solid transparent}
.verdict.ok{background:var(--ok-soft);color:var(--ok);border-color:color-mix(in srgb,var(--ok) 35%,transparent)}
.verdict.ng{background:var(--ng-soft);color:var(--ng);border-color:color-mix(in srgb,var(--ng) 35%,transparent)}
.verdict.warn{background:var(--warn-soft);color:var(--warn);border-color:color-mix(in srgb,var(--warn) 35%,transparent)}
.verdict b{display:block;margin-bottom:.15rem}
.step-item{border:1px solid var(--border);border-radius:var(--radius-sm);padding:.6rem .7rem;margin-bottom:.55rem;background:var(--surface-2)}
.step-item .step-head{display:flex;gap:.45rem;align-items:center;margin-bottom:.35rem;font-size:.82rem;font-weight:700;color:var(--text-soft)}
.step-item .nums{width:22px;height:22px;border-radius:50%;background:var(--accent-soft);color:var(--accent);display:grid;place-items:center;font-size:.76rem}
.step-item.correct{border-color:color-mix(in srgb,var(--ok) 45%,var(--border))}
.step-item.wrong{border-color:color-mix(in srgb,var(--ng) 45%,var(--border))}
.blank-row{display:grid;grid-template-columns:1fr auto;gap:.5rem;align-items:center;padding:.45rem 0;border-bottom:1px dashed var(--border)}
.blank-row:last-child{border-bottom:0}
.blank-row .blank-label{font-size:.9rem}
.blank-row .blank-input{width:150px}
.blank-row .blank-input.wide{width:100%}
.opt-list{display:flex;gap:.3rem;flex-wrap:wrap;margin-top:.25rem}
.opt-list button{border:1px solid var(--border-strong);background:var(--surface);border-radius:8px;padding:.2rem .55rem;font-size:.82rem;cursor:pointer;font-family:var(--mono)}
details.explain{border:1px solid var(--border);border-radius:var(--radius-sm);margin-bottom:.6rem;background:var(--surface)}
details.explain > summary{
  cursor:pointer;padding:.6rem .8rem;font-weight:700;font-size:.9rem;list-style:none;
  display:flex;align-items:center;gap:.4rem
}
details.explain > summary::-webkit-details-marker{display:none}
details.explain > summary::before{content:"▸";color:var(--muted);transition:.15s;display:inline-block}
details.explain[open] > summary::before{transform:rotate(90deg)}
details.explain .body{padding:0 .95rem .9rem;font-size:.93rem;border-top:1px solid var(--border);padding-top:.75rem}
.alt-card{border:1px solid var(--border);border-radius:var(--radius-sm);padding:.8rem;margin-bottom:.6rem;background:var(--surface-2)}
.alt-card h4{margin:0 0 .4rem;font-size:.95rem;color:var(--accent-2)}
.rubric{border-left:3px solid var(--accent);padding-left:.7rem;margin:.5rem 0}
.rubric li{font-size:.87rem}
.side-panel{position:sticky;top:calc(var(--header-h) + 10px);display:flex;flex-direction:column;gap:.8rem}
@media(max-width:1000px){.side-panel{position:static}}
.mini-note{height:230px;border-radius:10px;overflow:hidden;border:1px solid var(--border);background:var(--surface)}
.palette{display:flex;gap:.3rem;flex-wrap:wrap}
.swatch{width:24px;height:24px;border-radius:7px;border:2px solid var(--border);cursor:pointer}
.swatch.active{border-color:var(--accent);box-shadow:0 0 0 2px var(--accent-soft)}

/* ---------- notes ---------- */
.note-shell{display:grid;grid-template-columns:250px minmax(0,1fr);gap:1rem;align-items:start}
@media(max-width:900px){.note-shell{grid-template-columns:1fr}}
.note-list{max-height:62vh;overflow:auto}
.note-list .item{
  display:block;width:100%;text-align:left;border:1px solid var(--border);background:var(--surface);
  border-radius:10px;padding:.5rem .6rem;margin-bottom:.4rem;cursor:pointer;font:inherit;font-size:.86rem
}
.note-list .item.active{border-color:var(--accent);background:var(--accent-soft)}
.note-list .item b{display:block;font-size:.88rem;color:var(--text)}
.note-list .item span{color:var(--muted);font-size:.74rem}
.board-wrap{position:relative;border:1px solid var(--border);border-radius:var(--radius);background:var(--surface);overflow:hidden}
.board-canvas{display:block;width:100%;height:62vh;min-height:340px;touch-action:none;cursor:crosshair}
.board-canvas.pan{cursor:grab}
.board-canvas.pan:active{cursor:grabbing}
.board-toolbar{
  display:flex;gap:.5rem;flex-wrap:wrap;align-items:center;padding:.5rem .6rem;
  border-bottom:1px solid var(--border);background:var(--surface-2);font-size:.84rem
}
.board-toolbar .grp{display:flex;gap:.25rem;align-items:center;padding-right:.5rem;border-right:1px solid var(--border)}
.board-toolbar .grp:last-child{border-right:0;padding-right:0}
.paper-btn{border:1px solid var(--border-strong);background:var(--surface);border-radius:8px;padding:.22rem .5rem;font-size:.78rem;cursor:pointer}
.paper-btn.active{background:var(--accent);border-color:var(--accent);color:#fff}
.board-status{font-size:.74rem;color:var(--muted);padding:.3rem .65rem;border-top:1px solid var(--border);display:flex;justify-content:space-between}

/* ---------- graph ---------- */
.graph-wrap{position:relative;border:1px solid var(--border);border-radius:var(--radius);background:var(--surface);overflow:hidden}
.graph-canvas{display:block;width:100%;height:58vh;min-height:340px;touch-action:none;cursor:grab}
.graph-canvas:active{cursor:grabbing}
.graph-hud{position:absolute;right:8px;bottom:8px;background:color-mix(in srgb,var(--surface) 88%,transparent);border:1px solid var(--border);border-radius:8px;padding:.2rem .5rem;font-family:var(--mono);font-size:.75rem}
.expr-list{display:flex;flex-direction:column;gap:.4rem}
.expr-row{display:grid;grid-template-columns:26px 1fr 34px;gap:.4rem;align-items:center}
.expr-row .dot{width:16px;height:16px;border-radius:50%;border:2px solid #fff;box-shadow:0 0 0 1px var(--border-strong)}

/* ---------- AI ---------- */
.ai-panel{border:1px solid var(--border);border-radius:var(--radius);background:var(--surface);display:flex;flex-direction:column;overflow:hidden}
.ai-log{max-height:420px;overflow:auto;padding:.8rem;display:flex;flex-direction:column;gap:.6rem;background:var(--surface-2)}
.msg{border-radius:12px;padding:.6rem .75rem;font-size:.9rem;max-width:94%;white-space:normal;word-break:break-word}
.msg.user{background:var(--accent);color:#fff;align-self:flex-end;border-bottom-right-radius:4px}
.msg.ai{background:var(--surface);border:1px solid var(--border);align-self:flex-start;border-bottom-left-radius:4px}
.msg.sys{background:var(--warn-soft);color:var(--warn);border:1px solid color-mix(in srgb,var(--warn) 30%,transparent);align-self:center;font-size:.82rem;max-width:100%}
.msg .tag{display:block;font-size:.68rem;opacity:.75;margin-bottom:.2rem;font-weight:700;letter-spacing:.04em}
.ai-input{display:flex;gap:.4rem;padding:.6rem;border-top:1px solid var(--border);align-items:flex-end}
.ai-input textarea{min-height:44px;max-height:140px}
.typing span{display:inline-block;width:6px;height:6px;border-radius:50%;background:var(--muted);margin-right:3px;animation:blink 1.2s infinite}
.typing span:nth-child(2){animation-delay:.2s}.typing span:nth-child(3){animation-delay:.4s}
@keyframes blink{0%,60%,100%{opacity:.25}30%{opacity:1}}

/* ---------- stats ---------- */
.bar{height:8px;border-radius:999px;background:var(--bg-soft);overflow:hidden}
.bar > i{display:block;height:100%;background:linear-gradient(90deg,var(--accent),var(--accent-2));border-radius:999px}
.kpi{background:var(--surface);border:1px solid var(--border);border-radius:var(--radius);padding:.8rem 1rem}
.kpi b{display:block;font-size:1.5rem;line-height:1.2}
.kpi span{font-size:.76rem;color:var(--muted)}
.spark{display:flex;align-items:flex-end;gap:3px;height:52px}
.spark i{flex:1;background:var(--accent-soft);border-radius:3px 3px 0 0;min-height:2px;position:relative}
.spark i.on{background:var(--accent)}

/* ---------- toast / modal ---------- */
.toast-root{position:fixed;left:50%;transform:translateX(-50%);bottom:18px;z-index:200;display:flex;flex-direction:column;gap:.4rem;align-items:center;pointer-events:none}
.toast{
  background:var(--text);color:var(--bg);padding:.5rem .9rem;border-radius:999px;font-size:.84rem;
  box-shadow:var(--shadow-lg);opacity:0;transform:translateY(8px);transition:.2s
}
.toast.show{opacity:1;transform:translateY(0)}
.modal-root{position:fixed;inset:0;z-index:150;background:rgba(12,16,36,.5);display:grid;place-items:center;padding:1rem;backdrop-filter:blur(3px)}
.modal-root[hidden]{display:none}
.modal{
  background:var(--surface);border-radius:var(--radius);border:1px solid var(--border);
  width:min(760px,100%);max-height:86vh;overflow:auto;box-shadow:var(--shadow-lg)
}
.modal header{display:flex;justify-content:space-between;align-items:center;padding:.8rem 1rem;border-bottom:1px solid var(--border);position:sticky;top:0;background:var(--surface);z-index:2}
.modal .modal-body{padding:1rem}
.modal footer{padding:.7rem 1rem;border-top:1px solid var(--border);display:flex;justify-content:flex-end;gap:.4rem;position:sticky;bottom:0;background:var(--surface)}

/* ---------- misc ---------- */
.progress-line{display:flex;align-items:center;gap:.5rem;font-size:.8rem;color:var(--muted)}
.progress-line .bar{flex:1}
.chips-select{display:flex;gap:.3rem;flex-wrap:wrap}
.chips-select .chip{font-size:.78rem}
.unit-card{display:flex;flex-direction:column;gap:.45rem;text-decoration:none;color:inherit}
.unit-card:hover{text-decoration:none;border-color:var(--border-strong);box-shadow:var(--shadow-lg)}
.unit-card .u-code{font-size:.72rem;font-weight:800;color:var(--accent);letter-spacing:.06em}
.unit-card h3{margin:0;font-size:1rem}
.unit-card p{margin:0;font-size:.82rem;color:var(--text-soft)}
.toc{list-style:none;padding:0;margin:0}
.toc a{display:block;padding:.32rem .5rem;border-radius:8px;font-size:.86rem;color:var(--text-soft)}
.toc a:hover{background:var(--bg-soft);text-decoration:none;color:var(--text)}
.section-nav{display:flex;justify-content:space-between;gap:.5rem;margin-top:1.2rem}
.empty{text-align:center;color:var(--muted);padding:2.4rem 1rem;font-size:.9rem}
.empty .big{font-size:2rem;display:block;margin-bottom:.3rem;opacity:.6}
.kbd{font-family:var(--mono);font-size:.75rem;border:1px solid var(--border-strong);border-bottom-width:2px;border-radius:5px;padding:0 .3rem;background:var(--surface-2)}
@media(max-width:720px){
  body{font-size:15px}
  .header-inner{flex-wrap:wrap;gap:.4rem;padding:.4rem .7rem}
  .main-nav{order:3;width:100%;flex-basis:100%}
  .app-main{padding:.8rem .7rem 2rem}
  h1{font-size:1.42rem}
  .brand-text small{display:none}
}
@media print{
  .site-header,.site-footer,.board-toolbar,.mode-chips,.answer-row,.btn{display:none!important}
  .work-layout{grid-template-columns:1fr}
  body{background:#fff}
}