/* v6 source-grounded proof labs: minimal editorial layout, real interaction states. */
.ad-head{border-bottom:1px solid var(--line);background:linear-gradient(115deg,var(--bg-soft),var(--panel));padding:38px 0 33px}
.ad-head .container>a{font-size:13px;font-weight:700;color:var(--accent);text-decoration:underline;text-underline-offset:3px}
.ad-head .container>span{font-size:12px;color:var(--muted)}
.ad-head h1{font-size:clamp(28px,4.1vw,45px);line-height:1.12;letter-spacing:-.028em;max-width:920px;margin:13px 0}
.ad-head p{font-size:15px;color:var(--muted);max-width:780px;line-height:1.7;margin-bottom:15px}
.ad-grid{display:grid;grid-template-columns:minmax(0,1fr) 272px;gap:26px;padding-top:31px;padding-bottom:78px;align-items:start}
.ad-main{background:var(--panel);border:1px solid var(--line);border-radius:15px;padding:29px 34px;min-width:0}
.ad-intro{background:var(--bg-soft);padding:20px 23px;border-radius:11px;border-left:3px solid var(--accent)}
.ad-intro h2,.ad-topic h2{font-size:23px;line-height:1.3;margin:0 0 12px;color:var(--ink)}
.ad-intro li{line-height:1.6;padding:3px 0;font-size:14px}
.ad-topic{padding:29px 0 25px;border-bottom:1px solid var(--line)}
.ad-topic>span{font-size:11px;letter-spacing:.09em;text-transform:uppercase;color:var(--accent);font-weight:750}
.ad-topic>span+h2{margin-top:7px}
.ad-topic p{line-height:1.84;font-size:15px;max-width:77ch;color:var(--text)}
.ad-topic .algo-code{margin:9px 0 0}
.ad-lab{margin:27px 0 7px;border:1px solid var(--line);border-radius:14px;overflow:hidden;background:var(--panel)}
.ad-top{padding:15px 19px;display:flex;justify-content:space-between;align-items:center;gap:12px;border-bottom:1px solid var(--line);background:var(--bg-soft)}
.ad-top small{font-size:11px;color:var(--muted)}
.ad-top h2{font-size:20px;margin:3px 0 0}
.ad-top>span{font-size:13px;font-variant-numeric:tabular-nums;color:var(--accent);font-weight:800}
.ad-canvas{background:#fff;color:#21314c;overflow-x:auto;padding:14px 12px}
.ad-canvas svg{width:100%;min-width:640px;height:auto;display:block}
.ad-controls{padding:13px 16px;border-top:1px solid var(--line);display:flex;align-items:center;gap:13px}
.ad-controls input{flex:1;min-width:42px;accent-color:#327aaf;cursor:pointer}
.ad-step,.ad-reveal{font:inherit;font-size:13px;font-weight:700;border-radius:8px;border:1px solid var(--line);background:var(--panel);color:var(--ink);padding:9px 12px;cursor:pointer}
.ad-step:hover:enabled,.ad-reveal:hover{border-color:var(--accent);background:var(--bg-soft)}
.ad-step:disabled{opacity:.38;cursor:default}
.ad-note{font-size:12px;line-height:1.7;color:var(--muted);padding:0 19px 11px}
.ad-reveal{margin:4px 0 8px}
#ad-proof-text,#ad-answer-text{padding:16px;background:var(--bg-soft);border-radius:9px;border:1px solid var(--line)}
.ad-sidebar{position:sticky;top:88px;border:1px solid var(--line);border-radius:12px;padding:20px;background:var(--panel);display:grid;gap:7px;max-height:calc(100vh - 100px);overflow-y:auto}
.ad-sidebar h3{font-size:16px;margin:7px 0 3px}
.ad-sidebar p{font-size:12px;line-height:1.68;color:var(--muted);margin:0 0 5px}
.ad-sidebar .bm-open-pdf{justify-self:start}
.ad-sidebar hr{height:1px;width:100%;background:var(--line);border:0;margin:12px 0}
.ad-sidebar a{padding:9px 10px;font-size:12px;line-height:1.45;color:var(--text);border-radius:7px}
.ad-sidebar a:hover,.ad-sidebar a.ad-active{background:var(--bg-soft);color:var(--accent)}
.ad-next{display:flex;flex-wrap:wrap;gap:15px;margin:27px 0 0}
.ad-next a{color:var(--accent);font-weight:700;text-decoration:underline;font-size:13px}
.ad-depth-preview p{font-size:14px}
.ad-card-row{display:grid;grid-template-columns:repeat(auto-fit,minmax(210px,1fr));gap:11px;margin:16px 0 6px}
.ad-card-row a{background:var(--bg-soft);border:1px solid var(--line);border-radius:10px;display:grid;gap:7px;padding:14px;min-width:0}
.ad-card-row a:hover{border-color:var(--accent)}
.ad-card-row b{font-size:11px;color:var(--accent)}
.ad-card-row strong{font-size:15px;color:var(--ink)}
.ad-card-row small{font-size:12px;color:var(--muted)}
@media(max-width:960px){.ad-grid{grid-template-columns:1fr}.ad-sidebar{position:static;max-height:none}}
@media(max-width:600px){.ad-head{padding:25px 0}.ad-grid{padding-top:14px}.ad-main{padding:17px 16px}.ad-topic{padding:22px 0}.ad-topic h2{font-size:20px}.ad-top{padding:12px}.ad-top h2{font-size:17px}.ad-controls{gap:6px;padding:11px}.ad-step{padding:9px 7px;font-size:11px}.ad-canvas{padding:5px 3px}}
/* Keep proof-lab accents consistent with the Algorithm Design course identity. */
.ad-head,.ad-grid{--accent:#6d58af}