:root{--bg:#f3f4f6;--surface:#fff;--border:#d1d5db;--text:#111827;--muted:#4b5563;--accent:#1d4ed8}*{box-sizing:border-box}body{color:var(--text);background:var(--bg);margin:0;font-family:Arial,Helvetica,sans-serif}.app-shell{grid-template-columns:300px 1fr;min-height:100vh;display:grid}.sidebar{background:var(--surface);border-right:1px solid var(--border);padding:1rem}.brand{margin:0 0 1rem;font-size:1.25rem}.tree-section+.tree-section{margin-top:.75rem}.tree-toggle{text-align:left;cursor:pointer;background:0 0;border:none;width:100%;padding:.35rem 0;font-size:1rem;font-weight:700}.tree-list{margin:.35rem 0 0;padding:0 0 0 .5rem;list-style:none}.tree-item{align-items:center;gap:.5rem;padding:.25rem 0;display:flex}.tree-item a{color:var(--text);text-transform:capitalize;text-decoration:none}.active a{color:var(--accent);font-weight:700}.content{place-items:center;padding:2rem;display:grid}.content-card{background:var(--surface);border:1px solid var(--border);border-radius:12px;width:min(720px,100%);padding:2rem}.content-card h2{margin-top:0}.content-card p{color:var(--muted);line-height:1.6}@media (max-width:900px){.app-shell{grid-template-columns:1fr}.sidebar{border-right:none;border-bottom:1px solid var(--border)}}