:root {
  --bg: #0f1115;
  --panel: #171a21;
  --border: #2a2e38;
  --text: #f2f3f5;
  --muted: #9aa1ac;
  --accent: #c0392b;
  --accent-hover: #a93226;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background: var(--bg);
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  display: flex;
  justify-content: center;
  padding: 24px 16px 64px;
}

.app {
  width: 100%;
  max-width: 900px;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 18px;
}

header {
  text-align: center;
}

h1 {
  margin: 0 0 6px;
  font-size: 1.8rem;
}

.subtitle {
  margin: 0;
  color: var(--muted);
  font-size: 0.95rem;
}

.toolbar {
  display: flex;
  flex-wrap: wrap;
  gap: 10px;
  justify-content: center;
}

.btn {
  appearance: none;
  border: 1px solid var(--border);
  background: var(--panel);
  color: var(--text);
  padding: 10px 18px;
  border-radius: 8px;
  font-size: 0.95rem;
  cursor: pointer;
  transition: background 0.15s ease, transform 0.05s ease;
  display: inline-flex;
  align-items: center;
  gap: 6px;
}

.btn:hover:not(:disabled) {
  background: #1f2330;
}

.btn:active:not(:disabled) {
  transform: translateY(1px);
}

.btn:disabled {
  opacity: 0.4;
  cursor: not-allowed;
}

.btn-primary {
  background: var(--accent);
  border-color: var(--accent);
}

.btn-primary:hover:not(:disabled) {
  background: var(--accent-hover);
}

.canvas-wrap {
  width: 100%;
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 200px;
  border: 2px dashed var(--border);
  border-radius: 12px;
  background: var(--panel);
  padding: 12px;
}

.placeholder {
  color: var(--muted);
  text-align: center;
  padding: 60px 20px;
  margin: 0;
}

.canvas-stack {
  position: relative;
  max-width: 100%;
  line-height: 0;
}

.canvas-stack canvas {
  max-width: 100%;
  height: auto;
  display: block;
}

#baseCanvas {
  border-radius: 6px;
}

#overlayCanvas {
  position: absolute;
  top: 0;
  left: 0;
  touch-action: none;
}

.hint {
  color: var(--muted);
  font-size: 0.85rem;
  text-align: center;
  margin: 0;
}