:root {
  --bg: #0e1620;
  --bg-grid: #17222f;
  --surface: #141e2a;
  --surface-2: #1b2734;
  --border: #2a3948;
  --border-strong: #3d5265;
  --text: #dfe8ef;
  --text-dim: #7c8b9a;
  --cyan: #4fd1c5;
  --cyan-dim: #245a56;
  --amber: #f2a93b;
  --red: #e8604c;
  --mono: "SF Mono", "Cascadia Code", Consolas, monospace;
}

* { box-sizing: border-box; }

html, body {
  margin: 0;
  height: 100%;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, "Segoe UI", Roboto, sans-serif;
  overflow: hidden;
}

/* ---------- top bar ---------- */

.topbar {
  height: 56px;
  display: flex;
  align-items: center;
  gap: 24px;
  padding: 0 18px;
  background: var(--surface);
  border-bottom: 1px solid var(--border);
}

.brand {
  font-family: var(--mono);
  font-size: 15px;
  letter-spacing: 0.5px;
  color: var(--text);
  white-space: nowrap;
}
.brand span { color: var(--cyan); }

.tool-group {
  display: flex;
  gap: 6px;
  flex: 1;
  overflow-x: auto;
}

.tool {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-dim);
  padding: 7px 14px;
  border-radius: 6px;
  font-size: 13px;
  cursor: pointer;
  white-space: nowrap;
}
.tool:hover { border-color: var(--border-strong); color: var(--text); }
.tool.active {
  background: var(--cyan-dim);
  border-color: var(--cyan);
  color: var(--cyan);
}

.right-controls {
  display: flex;
  align-items: center;
  gap: 14px;
}

.density-field {
  font-size: 12px;
  color: var(--text-dim);
  display: flex;
  align-items: center;
  gap: 8px;
  white-space: nowrap;
}
.density-field input {
  width: 76px;
  background: var(--surface-2);
  border: 1px solid var(--border);
  color: var(--text);
  font-family: var(--mono);
  font-size: 13px;
  padding: 5px 7px;
  border-radius: 5px;
}

.ghost-btn {
  background: transparent;
  border: 1px solid var(--border);
  color: var(--text-dim);
  padding: 8px 14px;
  border-radius: 6px;
  font-size: 13px;
  cursor: pointer;
}
.ghost-btn:hover { border-color: var(--red); color: var(--red); }

.solve-btn {
  background: var(--cyan);
  border: none;
  color: #06201d;
  font-weight: 500;
  padding: 9px 18px;
  border-radius: 6px;
  font-size: 13px;
  cursor: pointer;
}
.solve-btn:hover { filter: brightness(1.08); }
.solve-btn:disabled { opacity: 0.5; cursor: default; }

/* ---------- workspace ---------- */

.workspace {
  position: relative;
  height: calc(100vh - 56px);
}

#canvas {
  display: block;
  background-image:
    linear-gradient(var(--bg-grid) 1px, transparent 1px),
    linear-gradient(90deg, var(--bg-grid) 1px, transparent 1px);
  background-size: 28px 28px;
  cursor: crosshair;
}

.hint {
  position: absolute;
  top: 16px;
  left: 16px;
  font-size: 12px;
  color: var(--text-dim);
  background: rgba(20, 30, 42, 0.85);
  border: 1px solid var(--border);
  padding: 8px 12px;
  border-radius: 6px;
  pointer-events: none;
}

/* ---------- svg node/edge styling ---------- */

.node-circle {
  fill: var(--surface-2);
  stroke: var(--border-strong);
  stroke-width: 1.5;
  cursor: pointer;
}
.node-circle.fixed { fill: var(--cyan-dim); stroke: var(--cyan); }
.node-circle.selected { stroke: var(--amber); stroke-width: 2.5; }
.node-circle.connect-source { stroke: var(--amber); stroke-dasharray: 3 2; }

.node-label, .node-value {
  font-family: var(--mono);
  fill: var(--text);
  font-size: 11px;
  pointer-events: none;
  user-select: none;
}
.node-value { fill: var(--cyan); }

.edge-line {
  stroke: var(--border-strong);
  stroke-width: 2;
  cursor: pointer;
  fill: none;
}
.edge-line.selected { stroke: var(--amber); }
.edge-line.solved-flow { stroke: var(--amber); marker-end: url(#flow-arrow); }
.edge-line.solved-flow.reverse { marker-start: url(#flow-arrow); marker-end: none; }

.edge-hit {
  stroke: transparent;
  stroke-width: 16;
  cursor: pointer;
  fill: none;
}

.edge-label {
  font-family: var(--mono);
  font-size: 10px;
  fill: var(--text-dim);
  pointer-events: none;
  user-select: none;
}
.edge-label.solved { fill: var(--amber); }

marker path { fill: var(--amber); }

/* ---------- property panel ---------- */

.panel {
  position: absolute;
  top: 16px;
  right: 16px;
  width: 260px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
}
.panel.hidden { display: none; }

.panel-header {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 10px 14px;
  border-bottom: 1px solid var(--border);
  font-size: 13px;
  color: var(--text-dim);
}
#panel-close {
  background: none;
  border: none;
  color: var(--text-dim);
  font-size: 18px;
  cursor: pointer;
  line-height: 1;
}

#panel-body {
  padding: 14px;
  display: flex;
  flex-direction: column;
  gap: 12px;
}

.field label {
  display: block;
  font-size: 11px;
  color: var(--text-dim);
  margin-bottom: 4px;
}
.field input[type="text"],
.field input[type="number"] {
  width: 100%;
  background: var(--surface-2);
  border: 1px solid var(--border);
  color: var(--text);
  font-family: var(--mono);
  font-size: 13px;
  padding: 6px 8px;
  border-radius: 5px;
}
.field.checkbox-field {
  display: flex;
  align-items: center;
  gap: 8px;
}
.field.checkbox-field label { margin: 0; }

.delete-btn {
  width: calc(100% - 28px);
  margin: 0 14px 14px;
  background: transparent;
  border: 1px solid var(--red);
  color: var(--red);
  padding: 8px;
  border-radius: 6px;
  font-size: 12px;
  cursor: pointer;
}
.delete-btn:hover { background: rgba(232, 96, 76, 0.12); }

/* ---------- status toast ---------- */

.status {
  position: absolute;
  bottom: 18px;
  left: 50%;
  transform: translateX(-50%);
  padding: 10px 18px;
  border-radius: 6px;
  font-size: 13px;
  font-family: var(--mono);
  background: var(--surface);
  border: 1px solid var(--border);
  display: none;
}
.status.ok { border-color: var(--cyan); color: var(--cyan); display: block; }
.status.err { border-color: var(--red); color: var(--red); display: block; }

/* ---------- units page ---------- */

.units-page {
  position: fixed;
  inset: 0;
  background: var(--bg);
  z-index: 50;
  display: flex;
  justify-content: center;
  overflow-y: auto;
}
.units-page.hidden { display: none; }

.units-page-inner {
  width: 100%;
  max-width: 520px;
  padding: 48px 24px;
}

.units-page-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 8px;
}
.units-page-header h2 {
  font-family: var(--mono);
  font-size: 20px;
  font-weight: 500;
  margin: 0;
  color: var(--text);
}

.units-page-note {
  color: var(--text-dim);
  font-size: 13px;
  line-height: 1.6;
  margin: 0 0 28px;
}

.units-list {
  display: flex;
  flex-direction: column;
  gap: 1px;
  border: 1px solid var(--border);
  border-radius: 8px;
  overflow: hidden;
}

.units-row {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 14px 16px;
  background: var(--surface);
}
.units-row + .units-row { border-top: 1px solid var(--border); }

.units-row-label {
  font-size: 14px;
  color: var(--text);
}

.units-select {
  background: var(--surface-2);
  border: 1px solid var(--border);
  color: var(--cyan);
  font-family: var(--mono);
  font-size: 13px;
  padding: 6px 10px;
  border-radius: 5px;
  cursor: pointer;
}