/* Approved navigation: shared peripheral shell, 2026-10-24. */
.study-topbar{height:76px;display:flex;align-items:center;gap:32px;padding:0 32px;background:var(--panel);border-bottom:1px solid var(--line);position:sticky;top:0;z-index:20}
.study-topbar .logo{gap:10px}.study-topbar nav{display:flex;align-items:center;gap:8px;margin-left:auto}.study-topbar nav :is(a,button){display:flex;align-items:baseline;gap:8px;padding:8px 14px;border:0;background:transparent;color:var(--muted);font-size:12px;min-height:40px;border-radius:8px}.study-topbar nav :is(a,button) span{font-family:var(--font-ui);font-size:13px;font-weight:500}.study-topbar nav small{font-size:11px}.study-topbar nav :is(a,button).active{background:var(--soft);color:var(--accent)}
.study-shell .sidebar{width:160px;top:76px;padding:28px 16px;background:var(--bg);border-right:1px solid var(--line)}.study-shell main{margin-left:160px;padding:0 32px 28px;max-width:1700px}.rail-label{font-size:11px;color:var(--muted);letter-spacing:.04em;margin:0 0 18px}.study-shell .source{display:flex;flex-direction:column;align-items:stretch;gap:8px;margin:0}.study-shell .source :is(button,a){text-align:left;padding:12px 10px;min-width:0;width:100%;background:transparent;border-color:transparent;border-radius:8px}.study-shell .source :is(button,a) strong{font:500 13px/1.5 var(--font-ui);display:block}.study-shell .source :is(button,a) small{display:block;color:var(--muted);font-size:10px;margin-top:4px}.study-shell .source :is(button,a).active{background:var(--soft);color:var(--accent);box-shadow:inset 2px 0 var(--accent)}.study-shell .source>span{font-size:10px;line-height:1.8;text-align:left;margin:20px 0 0;flex:none}.library-home{font-size:11px;color:var(--muted);margin-top:auto;padding-top:24px}.study-shell .heading{padding:24px 0}.study-shell #subject-icon{font-size:40px}
.study-shell .source :is(button,a){display:block}
@media(max-width:1100px) and (min-width:701px){.study-shell .sidebar{width:148px;padding:24px 12px}.study-shell main{margin-left:148px;padding-left:24px;padding-right:24px}}
@media(max-width:700px){.study-topbar{height:66px;padding:0 16px;gap:12px}.study-topbar .logo>span{display:none}.study-topbar .logo b{width:32px;height:36px;font-size:16px}.study-topbar nav{gap:0;flex:1;justify-content:center;min-width:0}.study-topbar nav :is(a,button){padding:7px 9px;min-height:40px;gap:0}.study-topbar nav small{display:none}.study-topbar nav :is(a,button) span{font-size:12px}.study-topbar #theme{width:36px;height:36px;min-width:36px;min-height:36px}.study-shell .sidebar{position:static;width:auto;padding:16px 20px;border-right:0;border-bottom:1px solid var(--line);display:block}.rail-label{display:none}.study-shell .source{flex-direction:row;gap:8px}.study-shell .source :is(button,a){padding:8px;flex:1}.study-shell .source :is(button,a) strong{font-size:11px}.study-shell .source :is(button,a) small{font-size:9px}.study-shell .source>span,.library-home{display:none}.study-shell main{margin:0;padding:0 20px 24px}.study-shell .heading{padding:20px 0}}

/* Shell applies only to peripheral documents opting into study-shell. */
.study-shell .study-topbar nav :is(a,button){box-sizing:border-box;text-decoration:none;white-space:nowrap}.study-shell .study-topbar .logo{flex-shrink:0}.study-shell .study-topbar #theme{flex-shrink:0}.study-shell main{min-width:0}
@media(max-width:360px){.study-shell .study-topbar{padding-inline:10px;gap:6px}.study-shell .study-topbar nav :is(a,button){padding-inline:6px}}