:root{--bg:#0f1720;--panel:#111827;--border:#1f2937;--text:#e5e7eb;--muted:#9ca3af;--accent:#3b82f6;--added:#063b22;--removed:#3b0a0a;--changed:#3b2f0a}*{box-sizing:border-box}body,html{margin:0;padding:0;background:var(--bg);color:var(--text);font-family:ui-sans-serif,system-ui,-apple-system,Segoe UI,Roboto}.toolbar{display:flex;align-items:center;gap:10px;padding:10px 14px;border-bottom:1px solid var(--border);background:linear-gradient(180deg,#0b1220,#0a1020);box-shadow:inset 0 -1px 0 hsla(0,0%,100%,.03)}.toolbar-group{display:flex;gap:6px;padding:2px;background:#0f172a;border:1px solid var(--border);border-radius:10px}.toolbar-spacer{flex:1 1}.btn{height:30px;padding:0 12px;border-radius:8px;border:1px solid transparent;background:transparent;color:var(--text);font-size:13px;cursor:pointer}.btn:hover{background:#111827;border-color:#334155}.btn.subtle{color:var(--muted)}.btn.subtle:hover{color:var(--text)}.container{display:grid;grid-template-columns:1fr 1fr;height:calc(100vh - 44px)}.panel{border-right:1px solid var(--border);display:flex;flex-direction:column}.panel:last-child{border-right:none}.panel-head{display:flex;justify-content:space-between;align-items:center;padding:8px 10px;border-bottom:1px solid var(--border);background:#0b1220}.toggle{display:flex;gap:4px}.toggle button{padding:4px 8px;border-radius:6px;border:1px solid var(--border);background:#0b1220;color:var(--muted);cursor:pointer}.toggle .active{color:var(--text);border-color:#334155}.editor,.preview{flex:1 1;overflow:auto;padding:14px}textarea{width:100%;height:100%;color:var(--text);border:none;outline:none;resize:none;font-family:ui-monospace,SFMono-Regular,Menlo,monospace;font-size:13px;line-height:1.5}.preview,textarea{background:var(--panel)}.preview h1,h2,h3{border-bottom:1px solid var(--border);padding-bottom:4px}.diff-added{background:var(--added)}.diff-removed{background:var(--removed);text-decoration:line-through}.diff-changed{background:var(--changed)}.segmented{display:flex;height:30px;border:1px solid var(--border);border-radius:10px;overflow:hidden;background:#0f172a}.segmented button{padding:0 14px;border:none;background:transparent;color:var(--muted);font-size:13px;cursor:pointer}.segmented button.active{background:#1e293b;color:var(--text)}