:root {
  --space-1: 4px;
  --space-2: 8px;
  --space-3: 12px;
  --space-4: 16px;
  --space-5: 24px;
  --space-6: 32px;
  --space-7: 48px;
  --space-8: 64px;

  --text-xs: 12px;
  --text-sm: 13px;
  --text-base: 14px;
  --text-md: 16px;
  --text-lg: 20px;
  --text-xl: 24px;
  --text-2xl: 32px;

  --weight-normal: 400;
  --weight-medium: 500;

  --leading-body: 1.6;
  --leading-heading: 1.3;

  --radius-sm: 8px;
  --radius-md: 12px;
  --radius-lg: 16px;
  --radius-pill: 999px;

  --duration-fast: 120ms;
  --duration-base: 200ms;
  --ease: cubic-bezier(0.2, 0, 0.2, 1);

  --z-base: 0;
  --z-sticky: 10;
  --z-dropdown: 20;
  --z-overlay: 30;
  --z-modal: 40;
  --z-toast: 50;

  --font-sans: -apple-system, "Segoe UI", "PingFang SC", "Microsoft YaHei", sans-serif;
  --font-mono: ui-monospace, "Cascadia Code", Consolas, monospace;
}

:root,
[data-theme="light"] {
  --color-bg-page: #f7f7f5;
  --color-bg-surface: #ffffff;
  --color-bg-subtle: #f1efe8;
  --color-bg-inverse: #2c2c2a;

  --color-text-primary: #2c2c2a;
  --color-text-secondary: #5f5e5a;
  --color-text-tertiary: #6f6e6a;
  --color-text-inverse: #ffffff;

  --color-border-subtle: rgba(0, 0, 0, 0.08);
  --color-border-default: rgba(0, 0, 0, 0.15);
  --color-border-strong: rgba(0, 0, 0, 0.3);

  --color-accent: #185fa5;
  --color-accent-hover: #0c447c;
  --color-accent-subtle: #e6f1fb;
  --color-on-accent: #ffffff;

  --color-success: #0f6e56;
  --color-success-subtle: #e1f5ee;
  --color-warning: #854f0b;
  --color-warning-subtle: #faeeda;
  --color-danger: #a32d2d;
  --color-danger-subtle: #fcebeb;

  --color-focus-ring: #185fa5;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.06);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.08);
}

[data-theme="dark"] {
  --color-bg-page: #1b1b19;
  --color-bg-surface: #262624;
  --color-bg-subtle: #2f2f2c;
  --color-bg-inverse: #f1efe8;

  --color-text-primary: #f1efe8;
  --color-text-secondary: #b4b2a9;
  --color-text-tertiary: #9a9890;
  --color-text-inverse: #2c2c2a;

  --color-border-subtle: rgba(255, 255, 255, 0.1);
  --color-border-default: rgba(255, 255, 255, 0.18);
  --color-border-strong: rgba(255, 255, 255, 0.32);

  --color-accent: #85b7eb;
  --color-accent-hover: #b5d4f4;
  --color-accent-subtle: #0c447c;
  --color-on-accent: #042c53;

  --color-success: #5dcaa5;
  --color-success-subtle: #085041;
  --color-warning: #ef9f27;
  --color-warning-subtle: #633806;
  --color-danger: #f09595;
  --color-danger-subtle: #791f1f;

  --color-focus-ring: #85b7eb;
  --shadow-sm: 0 1px 2px rgba(0, 0, 0, 0.4);
  --shadow-md: 0 4px 12px rgba(0, 0, 0, 0.5);
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  background: var(--color-bg-page);
  color: var(--color-text-primary);
  font-family: var(--font-sans);
  font-size: var(--text-base);
  font-weight: var(--weight-normal);
  line-height: var(--leading-body);
}

h1, h2, h3, h4 {
  margin: 0;
  font-weight: var(--weight-medium);
  line-height: var(--leading-heading);
}

h1 { font-size: var(--text-2xl); }
h2 { font-size: var(--text-xl); }
h3 { font-size: var(--text-lg); }
h4 { font-size: var(--text-md); }

p { margin: 0; }

:focus-visible {
  outline: 2px solid var(--color-focus-ring);
  outline-offset: 2px;
}

button,
a,
input,
select,
textarea {
  font: inherit;
  color: inherit;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: var(--space-2);
  min-height: 44px;
  padding: 0 var(--space-4);
  border: 1px solid transparent;
  border-radius: var(--radius-sm);
  font-size: var(--text-base);
  font-weight: var(--weight-medium);
  cursor: pointer;
  transition: background var(--duration-fast) var(--ease);
}

.btn:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

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

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

.btn-secondary {
  background: var(--color-bg-surface);
  border-color: var(--color-border-default);
  color: var(--color-text-primary);
}

.btn-secondary:hover:not(:disabled) {
  border-color: var(--color-border-strong);
}

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

.btn-ghost:hover:not(:disabled) {
  background: var(--color-bg-subtle);
  color: var(--color-text-primary);
}

.card {
  padding: var(--space-5);
  background: var(--color-bg-surface);
  border: 1px solid var(--color-border-default);
  border-radius: var(--radius-md);
}

.field {
  display: flex;
  flex-direction: column;
  gap: var(--space-2);
}

.field-label {
  font-size: var(--text-sm);
  font-weight: var(--weight-medium);
  color: var(--color-text-secondary);
}

.input {
  min-height: 44px;
  padding: 0 var(--space-3);
  background: var(--color-bg-surface);
  border: 1px solid var(--color-border-default);
  border-radius: var(--radius-sm);
  font-size: var(--text-base);
}

.input:focus-visible {
  border-color: var(--color-accent);
  outline: 2px solid var(--color-focus-ring);
  outline-offset: 1px;
}

.input[aria-invalid="true"] {
  border-color: var(--color-danger);
}

.field-hint {
  font-size: var(--text-xs);
  color: var(--color-text-tertiary);
}

.field-error {
  font-size: var(--text-xs);
  color: var(--color-danger);
}

.stack {
  display: flex;
  flex-direction: column;
}

.stack-2 { gap: var(--space-2); }
.stack-3 { gap: var(--space-3); }
.stack-4 { gap: var(--space-4); }
.stack-5 { gap: var(--space-5); }
.stack-6 { gap: var(--space-6); }

.row {
  display: flex;
  align-items: center;
}

.row-2 { gap: var(--space-2); }
.row-3 { gap: var(--space-3); }
.row-4 { gap: var(--space-4); }

.muted { color: var(--color-text-secondary); }
.hint { color: var(--color-text-tertiary); font-size: var(--text-xs); }

.truncate {
  overflow: hidden;
  text-overflow: ellipsis;
  white-space: nowrap;
}

.skeleton {
  background: var(--color-bg-subtle);
  border-radius: var(--radius-sm);
  animation: pulse 1.2s var(--ease) infinite;
}

@media (prefers-reduced-motion: no-preference) {
  @keyframes pulse {
    0%, 100% { opacity: 1; }
    50% { opacity: 0.55; }
  }
}

@media (prefers-reduced-motion: reduce) {
  * {
    animation: none !important;
    transition: none !important;
  }
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}