:root{
  --navy:#002060; --navy-2:#0a2f7a; --red:#C8102E; --light:#EFF3F9; --line:#dfe5ef;
  --ink:#1a1a1a; --muted:#5a6478; --bg:#f4f6fb;
}
*{ box-sizing:border-box; }
html{ -webkit-text-size-adjust:100%; }
body{ margin:0; font-family:"Segoe UI", Aptos, Calibri, Arial, sans-serif; background:var(--bg); color:var(--ink); }
header{ background:var(--navy); color:#fff; padding:10px 24px; }
header .head{ max-width:1600px; margin:0 auto; }
header h1{ margin:0; font-size:1.3rem; letter-spacing:.3px; }
header p{ display:none; }
main{ max-width:1600px; margin:12px auto 24px; padding:0 16px; }
[hidden]{ display:none !important; }
.panel{ background:#fff; border-radius:14px; box-shadow:0 2px 10px rgba(0,32,96,.08); }

.bar{ display:flex; flex-wrap:wrap; align-items:center; gap:8px 12px; padding:10px 12px; margin-bottom:12px; }
.tabs{ display:flex; flex-wrap:wrap; gap:4px; padding:3px; background:var(--light); border-radius:11px; }
.tab{ font:inherit; font-size:.95rem; font-weight:800; border:0; background:none; color:var(--navy); padding:7px 16px; border-radius:8px; cursor:pointer; white-space:nowrap; }
.tab:hover{ background:#dfe7f3; }
.tab[aria-selected="true"]{ background:var(--navy); color:#fff; box-shadow:0 1px 4px rgba(0,32,96,.25); }
.shapes{ display:flex; flex-wrap:wrap; gap:6px; min-width:0; flex:1 1 300px; }
.shp, .meth{ font:inherit; font-size:.88rem; font-weight:700; min-height:34px; padding:4px 12px; border-radius:999px; border:1.5px solid #cfd8e8; background:#fff; color:var(--navy); cursor:pointer; }
.shp:hover, .meth:hover{ background:var(--light); }
.shp[aria-pressed="true"]{ background:var(--navy); border-color:var(--navy); color:#fff; }
.meth[aria-pressed="true"]{ background:#e7eefb; border-color:var(--navy); }

.work{ display:grid; grid-template-columns:minmax(0, 1fr) 380px; gap:14px; align-items:start; }
.board{ padding:10px 12px 12px; min-width:0; }
.btitle{ display:flex; align-items:center; flex-wrap:wrap; gap:6px 12px; padding:2px 4px 8px; }
.btitle h2{ margin:0; font-size:1.2rem; color:var(--navy); }
.methods{ display:flex; flex-wrap:wrap; gap:6px; }
.methods::before{ content:"Method:"; font-size:.74rem; font-weight:800; text-transform:uppercase; letter-spacing:.5px; color:var(--muted); align-self:center; }
.methods.one::before{ content:"Method:"; }
#stage{ display:block; width:100%; height:auto; aspect-ratio:800/440; background:#fff; border-radius:10px; border:1px solid var(--line); }
.stagewrap{ position:relative; }
#stage{ user-select:none; -webkit-user-select:none; }
#stage.turn{ touch-action:none; cursor:grab; }   /* (only the methods that can be turned and zoomed) */
#stage.turn.dragging{ cursor:grabbing; }
.viewbar{ position:absolute; top:8px; right:8px; display:flex; align-items:center; gap:4px; }
.vhint{ font-size:.74rem; font-weight:700; color:var(--muted); background:rgba(255,255,255,.85); padding:3px 7px; border-radius:7px; margin-right:2px; }
.vbtn{ font:inherit; font-size:1rem; font-weight:800; width:34px; height:34px; padding:0; border-radius:9px; border:1.5px solid #cfd8e8; background:rgba(255,255,255,.92); color:var(--navy); cursor:pointer; line-height:1; }
.vbtn:hover{ background:var(--light); border-color:var(--navy); }
.vbtn[hidden]{ display:none; }
/* labels: a thin white halo so they read over lines (none on shaded shapes: .nh) */
#stage text{ paint-order:stroke; stroke:#fff; stroke-width:3px; stroke-linejoin:round; text-rendering:geometricPrecision; }
#stage text.nh{ stroke:none; }
#stage text.v{ font-family:"Cambria Math", Cambria, "Times New Roman", serif; font-style:italic; }
#stage text.w{ font-family:"Segoe UI", Aptos, Calibri, Arial, sans-serif; }

/* player: Play, steps and the drag bar */
.player{ display:flex; align-items:center; gap:10px; margin-top:10px; }
.btn{ font:inherit; font-size:.92rem; font-weight:800; height:42px; min-width:42px; padding:0 14px; border-radius:10px; border:1.5px solid var(--navy); background:#fff; color:var(--navy); cursor:pointer; white-space:nowrap; }
.btn:hover{ background:var(--light); }
.btn.play{ background:var(--navy); color:#fff; min-width:96px; }
.btn.play:hover{ background:var(--navy-2); }
.chip{ font:inherit; font-size:.82rem; font-weight:800; height:34px; padding:0 12px; border-radius:999px; border:1.5px solid #cfd8e8; background:#fff; color:var(--muted); cursor:pointer; white-space:nowrap; }
.chip::before{ content:""; display:inline-block; width:.8em; height:.8em; margin-right:.4em; border-radius:3px; border:2px solid currentColor; vertical-align:-.1em; }
.chip[aria-pressed="true"]{ background:#e7eefb; border-color:var(--navy); color:var(--navy); }
.chip[aria-pressed="true"]::before{ background:var(--navy); box-shadow:inset 0 0 0 2px #e7eefb; }
.slider{ position:relative; flex:1 1 auto; height:44px; cursor:pointer; touch-action:none; user-select:none; -webkit-user-select:none; outline:none; min-width:80px; }
.slider .track{ position:absolute; left:12px; right:12px; top:18px; height:8px; border-radius:999px; background:#dfe5ef; }
.slider .fill{ position:absolute; left:0; top:0; bottom:0; border-radius:999px; background:var(--red); }
.slider .tick{ position:absolute; top:-4px; width:2px; height:16px; margin-left:-1px; background:#9aa6bb; border-radius:1px; }
.slider .thumb{ position:absolute; top:50%; width:28px; height:28px; margin:-14px 0 0 -14px; border-radius:50%; background:#fff; border:3px solid var(--red); box-shadow:0 2px 6px rgba(0,0,0,.25); }
.slider:focus-visible .thumb{ outline:3px solid #7fa7e8; outline-offset:2px; }
.slider .track .thumb{ top:4px; }
.pct{ font-size:.85rem; font-weight:700; color:var(--muted); min-width:3.2em; text-align:right; font-variant-numeric:tabular-nums; }

.side{ display:flex; flex-direction:column; gap:10px; min-width:0; }
.card{ padding:12px 14px; min-width:0; }
.card h3{ margin:0 0 8px; font-size:.74rem; letter-spacing:.6px; text-transform:uppercase; color:var(--navy); }
.caption{ font-size:1.12rem; line-height:1.45; color:var(--ink); min-height:4.4em; margin:0; }
.formula{ font-size:1.35rem; color:var(--ink); min-height:2.2em; overflow-x:auto; overflow-y:hidden; }
.formula .fl{ display:flex; flex-wrap:wrap; align-items:baseline; gap:0 .35em; padding:3px 0; }
.formula .new{ color:var(--red); }
.formula .final{ display:inline-block; border:2.5px solid var(--red); border-radius:8px; padding:2px 8px; background:#fff5f6; }
.formula .empty{ font-size:.9rem; color:var(--muted); }
.steps{ margin:0; padding:0; list-style:none; display:flex; flex-direction:column; gap:4px; }
.stp{ font:inherit; font-size:.9rem; line-height:1.35; text-align:left; width:100%; border:0; border-left:4px solid #dfe5ef; background:none; color:var(--muted); padding:5px 8px; border-radius:0 8px 8px 0; cursor:pointer; }
.stp:hover{ background:var(--light); }
.stp.done{ color:var(--ink); border-left-color:#9aa6bb; }
.stp.cur{ color:var(--navy); font-weight:700; border-left-color:var(--red); background:#fff5f6; }
.stp b{ color:var(--red); margin-right:4px; }
#stage.no-notes .note{ display:none; }
.chip.speed{ min-width:7.2em; }
.chip.speed::before{ display:none; }
.explain[hidden]{ display:none; }
.caption .katex, .stp .katex, .shp .katex, .meth .katex, .btitle .katex{ white-space:nowrap; }
.explain summary{ cursor:pointer; font-size:.74rem; letter-spacing:.6px; text-transform:uppercase; font-weight:800; color:var(--navy); }
.explain ol{ margin:8px 0 0; padding-left:1.4em; display:flex; flex-direction:column; gap:7px; font-size:.95rem; line-height:1.5; color:var(--ink); }
.explain .katex{ font-size:1.05em; }

@media (max-width:1000px){ .work{ grid-template-columns:minmax(0, 1fr); } }
@media (max-width:560px){
  main{ padding:0 8px; }
  .bar{ padding:8px; }
  .board{ padding:8px; }
  .player{ flex-wrap:wrap; gap:8px; }
  .slider{ order:-1; flex:1 1 100%; }
  .btn.play{ flex:1 1 auto; }
  .caption{ font-size:1rem; }
  .formula{ font-size:1.15rem; }
  .vhint{ display:none; }
  .vbtn{ width:30px; height:30px; font-size:.9rem; }
}
@media print{ .player, .bar{ display:none !important; } }