:root {
  --bg: #eef1f6;
  --bg-accent-1: #e4ebfb;
  --bg-accent-2: #f3ecfb;
  --panel: #ffffff;
  --border: #e2e5ec;
  --border-strong: #cbd1dd;
  --text: #1a1d27;
  --text-muted: #6b7280;
  --accent: #4f6df5;
  --accent-hover: #3d59df;
  --accent-soft: #eef1ff;
  --shadow-color: 220 30% 15%;
  --radius-lg: 16px;
  --radius-md: 10px;
  --radius-sm: 7px;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: -apple-system, "Segoe UI", "PingFang SC", "Microsoft YaHei", system-ui, sans-serif;
  color: var(--text);
  background:
    radial-gradient(circle at 12% -10%, var(--bg-accent-1), transparent 45%),
    radial-gradient(circle at 90% 0%, var(--bg-accent-2), transparent 40%),
    var(--bg);
  min-height: 100vh;
}

.app {
  max-width: 1080px;
  margin: 0 auto;
  padding: 48px 20px 72px;
}

.app-header {
  text-align: center;
  margin-bottom: 32px;
}

.app-icon {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 52px;
  height: 52px;
  border-radius: 14px;
  background: linear-gradient(135deg, var(--accent), #8b6cf0);
  color: #fff;
  margin-bottom: 14px;
  box-shadow: 0 8px 20px -6px hsl(var(--shadow-color) / 0.45);
}

.app-header h1 {
  font-size: 1.75rem;
  letter-spacing: -0.02em;
  margin: 0 0 10px;
}

.subtitle {
  color: var(--text-muted);
  margin: 0 auto 14px;
  max-width: 560px;
  line-height: 1.55;
  font-size: 0.98rem;
}

.upload-zone {
  border: 2px dashed var(--border-strong);
  border-radius: var(--radius-lg);
  background: var(--panel);
  padding: 56px 20px;
  text-align: center;
  cursor: pointer;
  transition: border-color 0.18s ease, background 0.18s ease, transform 0.18s ease, box-shadow 0.18s ease;
  box-shadow: 0 1px 2px hsl(var(--shadow-color) / 0.04);
}

.upload-zone:hover {
  border-color: var(--accent);
  background: var(--accent-soft);
  transform: translateY(-1px);
  box-shadow: 0 12px 24px -12px hsl(var(--shadow-color) / 0.25);
}

.upload-zone.dragover {
  border-color: var(--accent);
  background: var(--accent-soft);
  box-shadow: 0 12px 24px -12px hsl(var(--shadow-color) / 0.3);
}

.upload-icon {
  color: var(--accent);
  margin-bottom: 10px;
}

.upload-title {
  font-size: 1.05rem;
  font-weight: 600;
  margin: 0 0 6px;
}

.upload-hint {
  color: var(--text-muted);
  margin: 0;
  font-size: 0.88rem;
}

.workspace {
  display: grid;
  grid-template-columns: 1fr 300px;
  gap: 20px;
  margin-top: 28px;
  align-items: start;
}

@media (max-width: 760px) {
  .workspace {
    grid-template-columns: 1fr;
  }
}

.canvas-panel,
.controls-panel {
  background: var(--panel);
  border: 1px solid var(--border);
  border-radius: var(--radius-lg);
  padding: 18px;
  box-shadow: 0 1px 2px hsl(var(--shadow-color) / 0.04), 0 12px 28px -18px hsl(var(--shadow-color) / 0.2);
}

.controls-panel {
  position: sticky;
  top: 20px;
}

.panel-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 14px;
  font-weight: 600;
  flex-wrap: wrap;
  gap: 8px;
}

.bg-toggle {
  display: flex;
  gap: 4px;
  background: var(--bg);
  padding: 3px;
  border-radius: 9px;
}

.bg-toggle-btn {
  border: none;
  background: transparent;
  color: var(--text-muted);
  font-size: 0.78rem;
  padding: 5px 11px;
  border-radius: 6px;
  cursor: pointer;
  transition: background 0.15s ease, color 0.15s ease;
}

.bg-toggle-btn:hover {
  color: var(--text);
}

.bg-toggle-btn.active {
  background: var(--panel);
  color: var(--text);
  box-shadow: 0 1px 3px hsl(var(--shadow-color) / 0.15);
  font-weight: 600;
}

.canvas-wrap {
  border-radius: var(--radius-md);
  overflow: auto;
  display: flex;
  align-items: center;
  justify-content: center;
  min-height: 320px;
  max-height: 68vh;
  border: 1px solid var(--border);
}

.canvas-wrap.bg-checker {
  background-image:
    linear-gradient(45deg, #d5d9e1 25%, transparent 25%),
    linear-gradient(-45deg, #d5d9e1 25%, transparent 25%),
    linear-gradient(45deg, transparent 75%, #d5d9e1 75%),
    linear-gradient(-45deg, transparent 75%, #d5d9e1 75%);
  background-size: 22px 22px;
  background-position: 0 0, 0 11px, 11px -11px, -11px 0px;
  background-color: #fafbfc;
}

.canvas-wrap.bg-white {
  background: #ffffff;
}

.canvas-wrap.bg-dark {
  background: #21242c;
}

#previewCanvas {
  max-width: 100%;
  height: auto;
  display: block;
  cursor: default;
}

#previewCanvas.eyedropper-active {
  cursor: crosshair;
}

.hint {
  color: var(--text-muted);
  font-size: 0.8rem;
  margin: 12px 0 0;
  line-height: 1.5;
}

.hint strong {
  color: var(--text);
}

.control-group {
  margin-bottom: 22px;
}

.control-group:last-child {
  margin-bottom: 0;
}

.control-group label,
.control-label {
  display: block;
  font-size: 0.85rem;
  font-weight: 600;
  margin-bottom: 10px;
}

.label-hint {
  font-weight: 400;
  color: var(--text-muted);
}

.control-group input[type="range"] {
  width: 100%;
  height: 6px;
  border-radius: 999px;
  background: var(--border);
  appearance: none;
  -webkit-appearance: none;
  outline: none;
  cursor: pointer;
}

.control-group input[type="range"]::-webkit-slider-thumb {
  appearance: none;
  -webkit-appearance: none;
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: var(--accent);
  border: 3px solid #fff;
  box-shadow: 0 1px 4px hsl(var(--shadow-color) / 0.4);
  cursor: pointer;
}

.control-group input[type="range"]::-moz-range-thumb {
  width: 18px;
  height: 18px;
  border-radius: 50%;
  background: var(--accent);
  border: 3px solid #fff;
  box-shadow: 0 1px 4px hsl(var(--shadow-color) / 0.4);
  cursor: pointer;
}

.bg-color-row {
  display: flex;
  align-items: center;
  gap: 10px;
  margin-bottom: 12px;
}

.bg-swatch {
  width: 26px;
  height: 26px;
  border-radius: 7px;
  border: 1px solid var(--border);
  display: inline-block;
  background: #fff;
  box-shadow: inset 0 0 0 1px hsl(var(--shadow-color) / 0.03);
}

.bg-swatch-text {
  font-size: 0.8rem;
  color: var(--text-muted);
  font-family: ui-monospace, "SFMono-Regular", Menlo, monospace;
}

.button-row {
  display: flex;
  gap: 8px;
}

.btn {
  border-radius: var(--radius-sm);
  border: 1px solid var(--border);
  padding: 10px 14px;
  font-size: 0.85rem;
  font-weight: 500;
  cursor: pointer;
  width: 100%;
  transition: background 0.15s ease, border-color 0.15s ease, transform 0.1s ease, box-shadow 0.15s ease;
  font-family: inherit;
}

.button-row .btn {
  flex: 1;
}

.btn-secondary {
  background: var(--panel);
  color: var(--text);
}

.btn-secondary:hover {
  border-color: var(--border-strong);
  background: var(--bg);
}

.btn-secondary.active {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
}

.btn-primary {
  background: var(--accent);
  border-color: var(--accent);
  color: #fff;
  font-weight: 600;
  margin-bottom: 8px;
  box-shadow: 0 8px 18px -8px hsl(var(--shadow-color) / 0.5);
}

.btn-primary:hover {
  background: var(--accent-hover);
  transform: translateY(-1px);
}

.btn-primary:active {
  transform: translateY(0);
}

.btn-tertiary {
  background: transparent;
  border-color: transparent;
  color: var(--text-muted);
}

.btn-tertiary:hover {
  color: var(--text);
  background: var(--bg);
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #14161c;
    --bg-accent-1: #1c2340;
    --bg-accent-2: #2a2038;
    --panel: #1c1f28;
    --border: #2b2f3a;
    --border-strong: #3a3f4d;
    --text: #edeef2;
    --text-muted: #9198a8;
    --accent: #6f8bff;
    --accent-hover: #8199ff;
    --accent-soft: #232a4a;
    --shadow-color: 220 60% 3%;
  }

  .canvas-wrap.bg-checker {
    background-image:
      linear-gradient(45deg, #333844 25%, transparent 25%),
      linear-gradient(-45deg, #333844 25%, transparent 25%),
      linear-gradient(45deg, transparent 75%, #333844 75%),
      linear-gradient(-45deg, transparent 75%, #333844 75%);
    background-color: #262a33;
  }

  .canvas-wrap.bg-white {
    background: #f2f3f5;
  }
}