:root{
  --bg: #EEF1F4;
  --bg-grid: #E4E9EE;
  --panel: #FFFFFF;
  --panel-2: #FAFBFC;
  --ink: #131A22;
  --ink-soft: #4B5560;
  --muted: #838E99;
  --border: #DCE2E8;
  --border-strong: #C7CFD7;
  --indigo: #3557E0;
  --indigo-soft: #EAEFFD;
  --indigo-dim: #C7D3F8;
  --coral: #FF5F3D;
  --coral-soft: #FFE7E0;
  --amber: #E8A23A;
  --amber-soft: #FCEFDA;
  --green: #1E9E6B;
  --green-soft: #E1F6EC;
  --violet: #8354E0;
  --violet-soft: #EFE7FD;
  --code-bg: #FBFCFD;
  --shadow-sm: 0 1px 2px rgba(19,26,34,0.06);
  --shadow-md: 0 6px 20px rgba(19,26,34,0.08);
  --shadow-lg: 0 16px 40px rgba(19,26,34,0.12);
  --radius: 14px;
  --radius-sm: 8px;
  --font-display: 'Space Grotesk', sans-serif;
  --font-body: 'Inter', sans-serif;
  --font-code: 'JetBrains Mono', monospace;
}

*{ box-sizing: border-box; }
html,body{ height:100%; }
body{
  margin:0;
  background:
    linear-gradient(var(--bg-grid) 1px, transparent 1px) 0 0/100% 28px,
    linear-gradient(90deg, var(--bg-grid) 1px, transparent 1px) 0 0/28px 100%,
    var(--bg);
  background-attachment: fixed;
  color: var(--ink);
  font-family: var(--font-body);
  -webkit-font-smoothing: antialiased;
}
::selection{ background: var(--indigo-dim); }
a{ color: inherit; }
button{ font-family: inherit; }
::-webkit-scrollbar{ width:10px; height:10px; }
::-webkit-scrollbar-thumb{ background: var(--border-strong); border-radius: 8px; }
::-webkit-scrollbar-track{ background: transparent; }

/* ---------- App shell ---------- */
.app{
  display:grid;
  grid-template-columns: 258px 1fr;
  min-height:100vh;
}

/* ---------- Sidebar ---------- */
.sidebar{
  background: var(--panel);
  border-right:1px solid var(--border);
  padding: 22px 16px 24px;
  position: sticky; top:0; height:100vh; overflow-y:auto;
}
.brand{
  display:flex; align-items:center; gap:10px;
  padding: 2px 6px 20px;
  border-bottom: 1px solid var(--border);
  margin-bottom: 16px;
}
.brand-mark{
  width:34px; height:34px; border-radius:9px;
  background: linear-gradient(145deg, var(--indigo), #2540B5);
  display:flex; align-items:center; justify-content:center;
  color:#fff; font-family: var(--font-code); font-weight:700; font-size:15px;
  box-shadow: var(--shadow-sm);
  flex-shrink:0;
}
.brand-text{ line-height:1.15; }
.brand-title{ font-family: var(--font-display); font-weight:700; font-size:15px; letter-spacing:-0.01em;}
.brand-sub{ font-size:11px; color:var(--muted); font-family: var(--font-code); }

.nav-group{ margin-bottom: 18px; }
.nav-group-label{
  font-size: 11px; font-weight:600; letter-spacing:.08em; text-transform:uppercase;
  color: var(--muted); padding: 0 10px 8px;
}
.nav-item{
  display:flex; align-items:center; gap:10px;
  width:100%; text-align:left; border:none; background:transparent;
  padding:9px 10px; border-radius:9px; cursor:pointer;
  font-size:13.5px; color: var(--ink-soft); font-weight:500;
  transition: background .15s ease, color .15s ease;
}
.nav-item:hover{ background: var(--panel-2); color: var(--ink); }
.nav-item.active{ background: var(--indigo-soft); color: var(--indigo); font-weight:600; }
.nav-item .dot{
  width:6px; height:6px; border-radius:50%; background: var(--border-strong); flex-shrink:0;
}
.nav-item.active .dot{ background: var(--indigo); }

/* ---------- Main ---------- */
.main{ padding: 24px 30px 40px; max-width: 1400px; }
.topbar{
  display:flex; align-items:flex-start; justify-content:space-between; gap:20px;
  margin-bottom:18px; flex-wrap:wrap;
}
.topbar-title{ font-family: var(--font-display); font-size: 26px; font-weight:700; letter-spacing:-0.01em; }
.topbar-desc{ color: var(--ink-soft); font-size:13.5px; max-width:640px; margin-top:4px; line-height:1.5; }
.badges{ display:flex; gap:8px; flex-wrap:wrap; margin-top:10px;}
.badge{
  font-family: var(--font-code); font-size:11.5px; font-weight:600;
  padding:4px 10px; border-radius:999px; border:1px solid var(--border);
  background: var(--panel); color: var(--ink-soft);
}
.badge.b-time{ color:var(--indigo); border-color: var(--indigo-dim); background: var(--indigo-soft); }
.badge.b-space{ color:var(--violet); border-color:#D9C9FA; background: var(--violet-soft); }

.category-pill{
  font-family: var(--font-code); font-size:11px; font-weight:600;
  padding:5px 11px; border-radius:999px; background: var(--panel-2);
  border:1px solid var(--border); color: var(--muted); align-self:flex-start;
}

/* ---------- Workspace grid ---------- */
.workspace{
  display:grid;
  grid-template-columns: minmax(360px, 1fr) minmax(380px, 1.15fr);
  gap:18px;
  margin-bottom:16px;
}
@media (max-width: 980px){ .workspace{ grid-template-columns: 1fr; } }

.panel{
  background: var(--panel);
  border:1px solid var(--border);
  border-radius: var(--radius);
  box-shadow: var(--shadow-sm);
  overflow:hidden;
  display:flex; flex-direction:column;
}
.panel-head{
  display:flex; align-items:center; justify-content:space-between;
  padding: 11px 16px;
  border-bottom:1px solid var(--border);
  background: var(--panel-2);
}
.panel-head-title{
  font-family: var(--font-code); font-size:12.5px; font-weight:600; color: var(--ink-soft);
  display:flex; align-items:center; gap:8px;
}
.traffic{ display:flex; gap:6px; }
.traffic span{ width:9px; height:9px; border-radius:50%; display:inline-block; }
.traffic .r{ background:#FF6259; } .traffic .y{ background:#FFBD2E; } .traffic .g{ background:#28C93F; }

/* ---------- Code panel ---------- */
.code-scroll{
  max-height: 560px; overflow-y:auto; overflow-x:auto;
  background: var(--code-bg);
}
.code-table{
  width:100%; border-collapse:collapse;
  font-family: var(--font-code); font-size:13px; line-height: 1.9;
}
.code-table tr{ position:relative; }
.code-table td.ln{
  width:38px; text-align:right; padding:0 10px 0 0;
  color: var(--muted); user-select:none; vertical-align:top;
  border-right:1px solid var(--border);
  background: var(--panel-2);
  position:relative;
}
.code-table td.src{
  padding:0 16px 0 14px; white-space:pre; color: var(--ink); vertical-align:top;
}
.code-table tr.exec td.src{ background: var(--indigo-soft); }
.code-table tr.exec td.ln{ background: var(--indigo-dim); color: var(--indigo); font-weight:700; }
.code-table tr.exec td.ln::after{
  content:"";
  position:absolute; right:-1px; top:50%; transform: translateY(-50%);
  border-top:6px solid transparent; border-bottom:6px solid transparent;
  border-left:7px solid var(--coral);
}
.code-table tr.exec td.src::before{
  content:"";
  position:absolute; left:0; top:0; bottom:0; width:3px; background: var(--coral);
}
.pc-chip{
  display:inline-flex; align-items:center; gap:5px;
  font-family: var(--font-code); font-size:10.5px; font-weight:700;
  color:#fff; background: var(--coral); padding:1px 7px; border-radius:5px;
  letter-spacing:.03em;
}
.tok-kw{ color:#B5289B; font-weight:600; }
.tok-type{ color:#3557E0; }
.tok-fn{ color:#0B7DAA; }
.tok-cm{ color:#8B98A5; font-style:italic; }
.tok-num{ color:#C2410C; }
.tok-str{ color:#1E9E6B; }

/* ---------- Viz panel ---------- */
.viz-body{
  flex:1; min-height: 420px; max-height:560px;
  display:flex; align-items:center; justify-content:center;
  padding: 18px; overflow:auto;
  background:
    radial-gradient(circle at 1px 1px, var(--border) 1px, transparent 1px) 0 0/22px 22px,
    var(--panel);
}
.viz-body svg{ max-width:100%; height:auto; }

/* ---------- Narration + vars ---------- */
.strip{
  background: var(--panel); border:1px solid var(--border); border-radius: var(--radius);
  padding:14px 18px; margin-bottom:16px; box-shadow: var(--shadow-sm);
  display:flex; gap:18px; align-items:flex-start; flex-wrap:wrap;
}
.strip-narration{ flex:1; min-width:280px; }
.strip-label{ font-family: var(--font-code); font-size:10.5px; font-weight:700; letter-spacing:.08em; color: var(--muted); text-transform:uppercase; margin-bottom:5px; }
.strip-text{ font-size: 14.5px; line-height:1.5; color: var(--ink); min-height:22px; }
.vars-wrap{ display:flex; flex-direction:column; gap:6px; min-width:200px; }
.vars-chips{ display:flex; flex-wrap:wrap; gap:6px; }
.var-chip{
  font-family: var(--font-code); font-size:12px; padding:3px 9px; border-radius:7px;
  background: var(--panel-2); border:1px solid var(--border); color: var(--ink-soft);
}
.var-chip b{ color: var(--indigo); font-weight:700; }

/* ---------- Controls ---------- */
.controls{
  background: var(--panel); border:1px solid var(--border); border-radius: var(--radius);
  padding:14px 18px; box-shadow: var(--shadow-sm);
  display:flex; align-items:center; gap:16px; flex-wrap:wrap;
}
.transport{ display:flex; align-items:center; gap:8px; }
.tbtn{
  width:38px; height:38px; border-radius:10px; border:1px solid var(--border);
  background: var(--panel-2); cursor:pointer; display:flex; align-items:center; justify-content:center;
  color: var(--ink-soft); transition: all .15s ease;
}
.tbtn:hover{ border-color: var(--indigo-dim); color: var(--indigo); background:var(--indigo-soft); }
.tbtn.primary{ width:46px; height:46px; background: var(--indigo); color:#fff; border-color:var(--indigo); }
.tbtn.primary:hover{ background:#2A46C4; color:#fff; }
.tbtn:disabled{ opacity:.4; cursor:not-allowed; }
.tbtn svg{ width:16px; height:16px; }
.tbtn.primary svg{ width:18px; height:18px; }

.step-counter{
  font-family: var(--font-code); font-size:12px; color: var(--muted);
  padding: 0 4px; min-width:86px; text-align:center;
}
.speed-wrap{ display:flex; align-items:center; gap:8px; font-size:12px; color:var(--muted); font-family: var(--font-code); }
.speed-wrap input[type=range]{ width:100px; accent-color: var(--indigo); }

.io-wrap{ display:flex; align-items:center; gap:10px; margin-left:auto; flex-wrap:wrap; }
.io-field label{ font-size:11px; color:var(--muted); font-family: var(--font-code); display:block; margin-bottom:3px; }
.io-field input{
  font-family: var(--font-code); font-size:13px; padding:7px 10px; border-radius:8px;
  border:1px solid var(--border); background: var(--panel-2); color: var(--ink); width:160px;
}
.io-field input:focus{ outline:none; border-color: var(--indigo); background:#fff; }
.io-apply{
  font-family: var(--font-body); font-weight:600; font-size:12.5px;
  background: var(--ink); color:#fff; border:none; padding:8px 14px; border-radius:8px; cursor:pointer;
  transition: transform .1s ease;
}
.io-apply:hover{ background:#000; }
.io-apply:active{ transform: scale(.96); }
.io-error{ color: var(--coral); font-size:11.5px; font-family: var(--font-code); }

/* ---------- Bars viz ---------- */
.bars-wrap{ display:flex; align-items:flex-end; gap:8px; height:340px; padding-top:40px; position:relative; }
.bar{
  width:46px; border-radius: 8px 8px 4px 4px; position:relative; display:flex; align-items:flex-end; justify-content:center;
  background: var(--indigo-soft); border: 1.5px solid var(--indigo-dim);
  transition: height .35s cubic-bezier(.4,0,.2,1), background .25s ease, border-color .25s ease, transform .25s ease;
}
.bar .val{
  position:absolute; top:-24px; font-family: var(--font-code); font-size:12.5px; font-weight:700; color: var(--ink-soft);
}
.bar .idx{ position:absolute; bottom:-22px; font-family: var(--font-code); font-size:10.5px; color: var(--muted); }
.bar .ptr{ position:absolute; top:-46px; font-family: var(--font-code); font-size:10px; font-weight:700; color: var(--coral); white-space:nowrap; }
.bar.compare{ background: var(--amber-soft); border-color: var(--amber); transform: translateY(-4px); }
.bar.swap{ background: var(--coral-soft); border-color: var(--coral); transform: translateY(-10px) scale(1.03); }
.bar.sorted{ background: var(--green-soft); border-color: var(--green); }
.bar.pivot{ background: var(--violet-soft); border-color: var(--violet); }
.bar.min{ background: var(--amber-soft); border-color: var(--amber); }
.bar.current{ background: var(--indigo-dim); border-color: var(--indigo); }
.bar.found{ background: var(--green-soft); border-color: var(--green); transform: translateY(-10px) scale(1.06); }
.bar.lo, .bar.hi{ border-color: var(--indigo); }
.bar.mid{ background: var(--coral-soft); border-color: var(--coral); transform: translateY(-6px); }

/* ---------- Tree viz ---------- */
.tree-svg text{ font-family: var(--font-code); fill: var(--ink); }
.tnode-box{ fill: var(--panel); stroke: var(--border-strong); stroke-width:1.5; }
.tnode-box.dividing{ fill: var(--indigo-soft); stroke: var(--indigo-dim); }
.tnode-box.merging, .tnode-box.calling{ fill: var(--amber-soft); stroke: var(--amber); }
.tnode-box.sorted-sub, .tnode-box.done{ fill: var(--green-soft); stroke: var(--green); }
.tnode-box.merged{ fill: var(--indigo-dim); stroke: var(--indigo); }
.tnode-box.base{ fill: var(--violet-soft); stroke: var(--violet); }
.tnode-box.waiting{ fill: var(--amber-soft); stroke: var(--amber); }
.tedge{ stroke: var(--border-strong); stroke-width:1.5; }

/* ---------- Call stack viz ---------- */
.frames-wrap{ display:flex; flex-direction:column-reverse; gap:8px; width:100%; max-width:360px; }
.frame{
  border-radius:10px; padding:10px 14px; border:1.5px solid var(--border-strong);
  background: var(--panel-2); font-family: var(--font-code); font-size:13px;
  display:flex; justify-content:space-between; align-items:center;
  transition: all .3s ease;
}
.frame.calling, .frame.waiting{ background: var(--amber-soft); border-color: var(--amber); }
.frame.base, .frame.done{ background: var(--green-soft); border-color: var(--green); }
.frame .fn{ color: var(--indigo); font-weight:700; }
.frame .res{ color: var(--ink-soft); }

/* ---------- Stack/Queue struct viz ---------- */
.struct-stack{ display:flex; flex-direction:column-reverse; gap:6px; align-items:center; width:140px; }
.slot{
  width:120px; height:44px; border-radius:9px; border:1.5px solid var(--border-strong);
  background: var(--panel-2); display:flex; align-items:center; justify-content:center;
  font-family: var(--font-code); font-weight:700; font-size:15px; color: var(--ink-soft);
  position:relative; transition: all .25s ease;
}
.slot.filled{ background: var(--indigo-soft); border-color: var(--indigo-dim); color: var(--indigo); }
.slot.top-slot::after{
  content:"TOP"; position:absolute; right:-46px; font-family: var(--font-code); font-size:10px; font-weight:700; color: var(--coral);
}
.struct-queue{ display:flex; gap:6px; align-items:center; }
.struct-queue .slot.front-slot::before{
  content:"FRONT"; position:absolute; top:-20px; font-size:9.5px; color: var(--indigo); font-weight:700;
}
.struct-queue .slot.rear-slot::after{
  content:"REAR"; position:absolute; bottom:-20px; font-size:9.5px; color: var(--coral); font-weight:700;
}

/* ---------- Linked list viz ---------- */
.ll-wrap{ display:flex; align-items:center; flex-wrap:wrap; gap:0; }
.ll-node{
  display:flex; border:1.5px solid var(--border-strong); border-radius:9px; overflow:hidden;
  background: var(--panel-2); font-family: var(--font-code); font-weight:700; font-size:14px;
}
.ll-node .v{ padding:10px 14px; color: var(--indigo); }
.ll-node .p{ padding:10px 10px; color: var(--muted); border-left:1px solid var(--border); font-size:11px; }
.ll-arrow{ width:34px; text-align:center; color: var(--muted); font-size:16px; }
.ll-head-label{ font-family: var(--font-code); font-size:10.5px; color: var(--indigo); font-weight:700; margin-bottom:6px; }

/* ---------- Tower of Hanoi viz ---------- */
.hanoi-wrap{ display:flex; gap:36px; align-items:flex-end; justify-content:center; padding-bottom:10px; }
.hanoi-peg{ display:flex; flex-direction:column; align-items:center; }
.hanoi-rod-area{
  width:140px; height:230px; position:relative; display:flex; flex-direction:column-reverse; align-items:center;
  border-bottom: 5px solid var(--border-strong); border-radius: 3px;
}
.hanoi-rod-area::before{
  content:""; position:absolute; bottom:0; left:50%; transform:translateX(-50%);
  width:10px; height:100%; background: var(--border-strong); border-radius:4px 4px 0 0; z-index:0;
}
.hanoi-disk{
  height:26px; border-radius:7px; margin-bottom:4px; z-index:1;
  display:flex; align-items:center; justify-content:center;
  font-family: var(--font-code); font-weight:700; font-size:12px; color:#fff;
  border: 1.5px solid rgba(0,0,0,0.08);
  transition: all .3s ease;
}
.hanoi-label{ margin-top:10px; font-family: var(--font-code); font-weight:700; font-size:13px; color: var(--ink-soft); }
.hanoi-label .peg-name{ color: var(--indigo); }

.custom-code-area{
  display:none; width:100%; min-height:520px; border:none; outline:none; resize:vertical;
  font-family: var(--font-code); font-size:13px; line-height:1.9; color: var(--ink);
  background: var(--code-bg); padding:14px 16px; box-sizing:border-box;
}
.custom-code-area::placeholder{ color: var(--muted); }
.code-table tr.exec.exec-error td.src{ background: var(--coral-soft); }
.code-table tr.exec.exec-error td.ln{ background: var(--coral); color:#fff; }
.io-error.has-error{ background: var(--coral-soft); border:1px solid var(--coral); border-radius:7px; padding:4px 9px; }
.console-box{
  background: var(--ink); color:#CDEFC1; font-family: var(--font-code); font-size:12.5px;
  border-radius:9px; padding:12px 14px; min-height:44px; white-space:pre-wrap; word-break:break-word;
  width:100%; box-sizing:border-box;
}
.custom-viz-section{ width:100%; }
.custom-viz-section + .custom-viz-section{ margin-top:16px; }
.custom-empty-hint{ color:var(--muted); font-family: var(--font-code); font-size:13px; text-align:center; max-width:320px; line-height:1.6; }

/* ---------- Footer note ---------- */
.footnote{ text-align:center; color: var(--muted); font-size:11.5px; margin-top:18px; font-family: var(--font-code); }