:root{--bg: #f5f5fa;--card: #ffffff;--text: #1e1e2f;--muted: #6e6e8c;--border: #d9d9ec;--radius: 12px;--transition: .25s ease;--shadow: 0 10px 30px -5px rgba(0, 0, 0, .1);--accent: #6366f1}.dark{--bg: #1e2230;--card: #2b2f4a;--text: #f0f3ff;--muted: #8b94b3;--border: #3a436c}.dark .exercise-card div[role=note]{color:#cbd5e1!important}.dark .exercise-card .section>div:last-child{color:#94a3b8!important}*{box-sizing:border-box}body{margin:0;font-family:system-ui,-apple-system,BlinkMacSystemFont,Segoe UI,Roboto,Helvetica Neue,Arial,sans-serif;background:var(--bg);color:var(--text);min-height:100vh}.app{max-width:1100px;margin:0 auto;padding:1rem 1rem 3rem;display:flex;flex-direction:column;gap:.5rem}header{display:flex;justify-content:space-between;align-items:center;flex-wrap:wrap;gap:.5rem}h1{margin:0;font-size:1.5rem}button{padding:6px 14px;border-radius:6px;border:1px solid transparent;cursor:pointer;font-size:.9rem;transition:background var(--transition),box-shadow var(--transition),transform .12s ease}button:hover{filter:brightness(1.05)}button:focus{outline:2px solid var(--accent);outline-offset:2px}button.primary{background:var(--accent);color:#fff;border-color:var(--accent)}.panel{display:flex;gap:1rem;flex:1}.left{flex:1.2;display:flex;flex-direction:column;gap:1rem}.right{flex:1;display:flex;flex-direction:column;gap:1rem}.tree-wrapper{background:var(--card);border:1px solid var(--border);border-radius:var(--radius);padding:12px;min-height:400px;position:relative;max-width:100%;min-width:300px;overflow:auto;box-shadow:0 20px 20px #0000001f}.node-row{display:inline-flex;align-items:center;gap:4px;padding:4px 8px;border-radius:6px;cursor:pointer;transition:background var(--transition);position:relative}.node-row:hover{background:#6464c814}.node-row.cwd{background:#648cff33;outline:2px solid rgba(100,140,255,.6);transition:background var(--transition),outline var(--transition)}.tree-container{font-size:.95rem;line-height:1.2}.shell{background:var(--card);padding:12px;border-radius:var(--radius);border:1px solid var(--accent);margin-bottom:4px;position:relative;box-shadow:0 20px 20px #0000001f;width:100%}.input-row{display:flex;align-items:center;gap:6px}.prompt{background:#00000008;padding:4px 8px;border-radius:4px;font-size:.9rem}.shell-input{flex:1;padding:6px 10px;border:1px solid var(--border);border-radius:6px;font-family:monospace;font-size:.95rem;background:transparent;color:var(--text)}.shell input:focus{outline:2px solid rgba(100,140,255,.8)}.shell button{padding:6px 12px;border:none;background:#648cffcc;color:#fff;border-radius:6px;cursor:pointer;font-size:.9rem}.error{margin-top:4px;color:#ff6b6b;font-size:.85rem}.info-block{background:var(--card);border:1px solid var(--border);border-radius:var(--radius);padding:12px;display:flex;flex-direction:column;gap:10px;box-shadow:0 20px 20px #0000001f}.exercise-card{box-shadow:0 20px 20px #0000001f}.section{display:flex;flex-direction:column;gap:6px}.label{font-weight:600;font-size:.9rem}.code-block{background:#0000000d;padding:8px 12px;border-radius:6px;font-family:monospace;overflow-x:auto;margin:0;border:1px solid rgba(0,0,0,.1);min-width:400px;max-width:600px;box-sizing:border-box}.subsection{margin-top:6px;padding-left:6px}.muted{color:var(--muted)}.hint{font-size:.75rem;padding:8px;background:#00000005;border-radius:6px}footer{margin-top:auto;font-size:.7rem;text-align:center;color:var(--muted)}kbd{background:#00000012;padding:2px 6px;border-radius:4px;font-size:.75rem;font-family:monospace}.visually-hidden{position:absolute!important;width:1px;height:1px;padding:0;margin:-1px;overflow:hidden;clip:rect(0 0 0 0);white-space:nowrap;border:0}.autocomplete-suggestions{margin-top:4px;border:1px solid var(--border);background:var(--card);border-radius:6px;max-width:100%;font-size:.9rem;overflow:hidden}.autocomplete-suggestions .suggestion{padding:6px 10px;cursor:pointer}.autocomplete-suggestions .suggestion:hover{background:#648cff1a}.tab-button{background:transparent;border:1px solid #aaa;border-radius:4px;padding:4px 10px;cursor:pointer;font-weight:400;transition:background var(--transition),box-shadow var(--transition);margin-right:4px;color:var(--text)}.tab-button.active{background:var(--accent);color:#fff;font-weight:700;border-color:var(--accent)}.tab-button.completed{position:relative}.tab-button.completed:after{content:"✓";position:absolute;top:-4px;right:-4px;background:#22c55e;color:#fff;font-size:.6em;width:16px;height:16px;border-radius:50%;display:flex;align-items:center;justify-content:center}@keyframes pop{0%{transform:scale(.8)}50%{transform:scale(1.3)}to{transform:scale(1)}}.exercise-checkmark{display:inline-block;transition:transform .15s ease}.exercise-checkmark.pop{animation:pop .35s ease}.app-description{margin-top:4px;color:var(--muted)}.tree-hint{font-size:.8rem;color:var(--muted);margin-bottom:8px}.tabs-container{margin-top:10px;margin-bottom:4px;display:flex;gap:6px}.exercise-order-note{font-size:.75em;margin-bottom:4px;color:#555}.exercise-list{padding-left:16px;margin-top:6px}.overall-summary{margin-top:8px;font-size:.95em;color:#666}.shell-hint{margin-top:8px}.cwd-explanation{margin-bottom:8px;color:var(--muted);font-size:.9em}.path-note{margin-top:8px;color:var(--muted);font-size:.9em}.output-block{padding:6px 12px;white-space:pre-wrap;font-family:monospace}.command-tooltip{position:absolute;top:110%;left:50%;transform:translate(-50%,4px);background:var(--card);color:var(--text);border:1px solid rgba(0,0,0,.15);padding:10px;border-radius:6px;box-shadow:0 6px 20px #0000001a;z-index:100;width:260px;font-size:.85em;white-space:pre-wrap}.dark .command-tooltip{background:#1f2937;color:#f5f5f5}.command-tooltip-title{font-weight:600;margin-bottom:4px}