:root{
  --bg:#0e1116; --card:#161b22; --text:#e6edf3; --muted:#9da7b3;
  --border:#2b3240; --accent:#3b82f6; --radius:14px; --shadow:0 10px 25px rgba(0,0,0,.35);
}
*{box-sizing:border-box}
html,body{height:100%}
body{margin:0;font-family:ui-sans-serif,system-ui,-apple-system,Segoe UI,Roboto,Arial;background:var(--bg);color:var(--text)}
.container{max-width:1000px;margin:24px auto;padding:0 16px}
.header h1{margin:0 0 6px 0;font-size:22px}
.muted{color:var(--muted)}
.card{margin-top:16px;background:var(--card);border:1px solid var(--border);border-radius:var(--radius);box-shadow:var(--shadow);padding:16px}
.section-title{font-size:16px;margin:0 0 10px 0}
.grid{display:grid;grid-template-columns:1fr 1fr;gap:16px}
@media (max-width:860px){ .grid{grid-template-columns:1fr} }
.row{display:flex;flex-wrap:wrap;gap:12px;align-items:center;margin:.25rem 0}
.checks{display:flex;flex-wrap:wrap;gap:10px}
label{display:inline-flex;align-items:center;gap:8px}
.btn{background:linear-gradient(180deg,var(--accent),#255bd6);color:#fff;border:none;border-radius:10px;padding:10px 14px;font-weight:700;cursor:pointer;box-shadow:var(--shadow)}
.btn:active{transform:translateY(1px)}
.math{margin-top:8px;font-size:1.1rem}
.tasks{margin:10px 0 0 18px; display:none}
.tasks li{margin:4px 0}
.solution-wrap{margin-top:10px}
.toggle{background:none;border:1px solid var(--border);color:var(--accent);padding:6px 10px;border-radius:10px;cursor:pointer}
.toggle[disabled]{opacity:.6;cursor:not-allowed}
.collapse{overflow:hidden;max-height:0;opacity:0;transform:translateY(-4px);transition:max-height .35s ease,opacity .25s ease,transform .25s ease;border-left:2px solid #2b3955;margin-top:6px;padding-left:10px}
.collapse.show{max-height:600px;opacity:1;transform:translateY(0)}
.solution{background:#0f1420;border:1px solid var(--border);border-radius:10px;padding:10px 12px;line-height:1.6}
.ggb-box{border:1px dashed var(--border);border-radius:12px;padding:8px}
#ggb-element{width:100%;height:540px}
.apex{font-size:.7em;vertical-align:super}
.code{font-family:ui-monospace,SFMono-Regular,Menlo,Consolas,monospace}