:root{--bg:#f6f8fc;--panel:#fff;--text:#1f2937;--muted:#6b7280;--primary:#5b7cfa;--primary-soft:#e9edff;--green:#22c55e;--red:#ef4444;--blue:#3b82f6;--border:#e5e7eb;--shadow:0 20px 45px rgba(31,41,55,.08);--radius:22px}*{box-sizing:border-box}body{margin:0;font-family:Inter,Segoe UI,Arial,sans-serif;background:var(--bg);color:var(--text)}a{text-decoration:none;color:inherit}.sidebar{position:fixed;inset:0 auto 0 0;width:280px;background:#fff;border-right:1px solid var(--border);padding:22px;z-index:5;transition:.25s;overflow-y:auto}.brand{display:flex;gap:12px;align-items:center;margin-bottom:25px}.brand-mark{width:44px;height:44px;border-radius:15px;background:linear-gradient(135deg,#5b7cfa,#8bd3dd);display:grid;place-items:center;color:#fff;font-weight:800}.brand span{display:block;color:var(--muted);font-size:12px;margin-top:3px}.sidebar nav{display:grid;gap:7px}.sidebar a{padding:12px 14px;border-radius:15px;color:#4b5563;font-weight:600}.sidebar a:hover,.sidebar a.active{background:var(--primary-soft);color:#3344b5}.main{margin-left:280px;padding:30px;min-height:100vh}.drawer-toggle{display:none;position:fixed;top:14px;left:14px;z-index:9;border:0;border-radius:12px;background:#fff;box-shadow:var(--shadow);font-size:22px;padding:8px 12px}.card{background:var(--panel);border:1px solid var(--border);border-radius:var(--radius);padding:24px;box-shadow:var(--shadow);margin-bottom:22px}.gradient-card{background:linear-gradient(135deg,#fff,#edf4ff)}.hero{display:grid;grid-template-columns:1.4fr .8fr;align-items:center;min-height:330px}.hero h1,.page-header h1{font-size:clamp(32px,4vw,56px);line-height:1.02;margin:8px 0 14px}.hero p,.page-header p{font-size:18px;color:var(--muted);max-width:760px}.eyebrow{letter-spacing:.14em;text-transform:uppercase;color:var(--primary)!important;font-size:12px!important;font-weight:800}.hero-actions,.inline-controls{display:flex;gap:10px;flex-wrap:wrap;align-items:center}.btn{border:0;background:#eef2f7;color:#1f2937;padding:11px 16px;border-radius:14px;font-weight:800;cursor:pointer;transition:.2s}.btn:hover{transform:translateY(-1px);filter:brightness(.98)}.btn.primary{background:var(--primary);color:#fff}.btn.danger{background:#fee2e2;color:#991b1b}.btn.success{background:#dcfce7;color:#166534}input,select,textarea{border:1px solid var(--border);border-radius:14px;padding:11px 13px;background:#fff;font:inherit;min-width:130px}textarea{width:100%;min-height:88px}.grid{display:grid;gap:22px}.cards-grid{grid-template-columns:repeat(3,minmax(0,1fr))}.two-col{grid-template-columns:1fr 1fr}.controls-card h2{margin-top:0}.stats{display:flex;gap:14px;flex-wrap:wrap;margin-top:18px}.stats span{background:#f8fafc;border:1px solid var(--border);border-radius:999px;padding:8px 13px;color:var(--muted)}.message{padding:14px;border-radius:15px;background:#f8fafc;border:1px dashed var(--border);color:#4b5563}.form-grid{display:grid;grid-template-columns:2fr 1fr 1fr;gap:16px;margin-bottom:15px}label small{display:block;color:var(--muted);margin:4px 0 6px}.table-wrap{overflow:auto}table{border-collapse:collapse;width:100%}th,td{padding:10px;border-bottom:1px solid var(--border);text-align:left}th{background:#f8fafc}.hero-visual{height:220px;position:relative}.floating-node{position:absolute;width:62px;height:62px;border-radius:20px;background:#fff;border:2px solid var(--primary);display:grid;place-items:center;font-weight:900;box-shadow:var(--shadow);animation:float 3.5s ease-in-out infinite}.floating-node:nth-child(1){left:20%;top:14%}.floating-node:nth-child(2){left:58%;top:2%;animation-delay:.4s}.floating-node:nth-child(3){left:38%;top:48%;animation-delay:.8s}.floating-node:nth-child(4){left:68%;top:58%;animation-delay:1.1s}@keyframes float{50%{transform:translateY(-12px)}}.stack-visual{display:flex;flex-direction:column-reverse;align-items:center;gap:8px;min-height:330px;justify-content:flex-start;border:2px dashed #dbe3f0;border-radius:20px;padding:18px}.stack-item,.array-item,.list-node,.tree-node{display:grid;place-items:center;font-weight:900;border-radius:16px;background:#fff;border:2px solid #dbe3f0;transition:.25s}.stack-item{width:140px;height:48px}.array-visual{display:flex;gap:12px;align-items:center;flex-wrap:wrap;min-height:90px}.array-item{width:56px;height:56px}.bar-visual{height:340px;display:flex;gap:12px;align-items:flex-end;justify-content:center;padding:20px;border:2px dashed #dbe3f0;border-radius:20px}.bar{width:48px;min-height:30px;background:#dbeafe;border:2px solid var(--blue);border-radius:14px 14px 6px 6px;display:flex;align-items:flex-start;justify-content:center;padding-top:7px;font-weight:900;transition:.25s}.compare{background:#dbeafe!important;border-color:var(--blue)!important}.swap{background:#fee2e2!important;border-color:var(--red)!important}.current{background:#dcfce7!important;border-color:var(--green)!important}.sorted{background:#ede9fe!important;border-color:#8b5cf6!important}.list-visual{display:flex;gap:10px;align-items:center;flex-wrap:wrap;min-height:110px}.list-node{width:66px;height:50px}.arrow{font-weight:900;color:#94a3b8}.tree-visual{min-height:260px;display:flex;align-items:center;justify-content:center;gap:12px;flex-wrap:wrap;border:2px dashed #dbe3f0;border-radius:20px;padding:18px}.tree-level{display:flex;justify-content:center;gap:22px;width:100%;margin:8px 0}.tree-node{width:54px;height:54px}.mini h3{margin-top:0}@media(max-width:900px){.sidebar{transform:translateX(-105%)}.sidebar.open{transform:translateX(0)}.drawer-toggle{display:block}.main{margin-left:0;padding:72px 16px 20px}.hero,.two-col,.cards-grid,.form-grid{grid-template-columns:1fr}.hero-visual{display:none}}

/* Improved binary tree / BST / heap visualizations */
.tree-canvas{min-height:420px;display:block;overflow:auto;padding:18px;background:#fff;}
.tree-svg{width:100%;min-width:520px;height:auto;display:block;}
.tree-edge{stroke:#cbd5e1;stroke-width:4;stroke-linecap:round;}
.tree-svg-node{fill:#fff;stroke:#dbe3f0;stroke-width:4;transition:.25s;filter:drop-shadow(0 8px 14px rgba(31,41,55,.08));}
.tree-svg-node.current{fill:#dcfce7;stroke:#22c55e;}
.tree-svg-text{font-size:17px;font-weight:900;fill:#1f2937;font-family:Inter,Segoe UI,Arial,sans-serif;pointer-events:none;}
.empty-state{min-height:240px;display:grid;place-items:center;color:#64748b;font-weight:800;border:2px dashed #dbe3f0;border-radius:18px;}
.definition-grid{display:grid;grid-template-columns:repeat(4,minmax(0,1fr));gap:14px;}
.definition-grid div{background:#f8fafc;border:1px solid var(--border);border-radius:18px;padding:16px;}
.definition-grid strong{display:block;color:#3344b5;margin-bottom:6px;font-size:16px;}
.definition-grid p{margin:0;color:#64748b;line-height:1.45;}
.definition-grid.compact{grid-template-columns:repeat(3,minmax(0,1fr));}
.array-item small{display:block;font-size:11px;color:#64748b;line-height:1;margin-bottom:4px;}
.array-item strong{font-size:18px;line-height:1;}
@media(max-width:900px){.definition-grid,.definition-grid.compact{grid-template-columns:1fr}.tree-canvas{min-height:320px}.tree-svg{min-width:460px}}