* {
  box-sizing: border-box;
}

:root {
  color-scheme: light dark;
}

html,
body {
  margin: 0;
  min-height: 100%;
}

body {
  position: relative;
  isolation: isolate;
  overflow-x: hidden;
  color: var(--pn-text-primary);
  font-family: var(--pn-font-main);
  font-size: var(--pn-font-size-body);
  line-height: var(--pn-line-height-body);
  background: var(--pn-bg);
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  font-feature-settings: "ss01", "cv11";
  text-rendering: optimizeLegibility;
  transition: background-color var(--pn-motion-base) var(--pn-ease-standard);
}

h1, h2, h3, h4, h5, h6 {
  color: var(--pn-text-primary);
  line-height: var(--pn-title-line-height);
  letter-spacing: var(--pn-title-letter-spacing);
  font-weight: 600;
  margin: 0;
}

a {
  color: var(--pn-accent);
  text-decoration: none;
  transition: opacity var(--pn-motion-fast) var(--pn-ease-standard);
}

a:hover {
  opacity: 0.8;
}

a:focus-visible {
  outline: 2px solid var(--pn-brand-500);
  outline-offset: 3px;
  border-radius: var(--pn-radius-sm);
}

::selection {
  background: rgba(0, 122, 255, 0.24);
  color: inherit;
}

@media (prefers-color-scheme: dark) {
  ::selection {
    background: rgba(10, 132, 255, 0.38);
  }
}

img, video {
  user-select: none;
  -webkit-user-drag: none;
}

input, button, select, textarea {
  font-family: inherit;
}

/* ———— Utility 类 ———— */
.u-hidden { display: none !important; }

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

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

.u-clamp-2,
.u-clamp-3 {
  display: -webkit-box;
  -webkit-box-orient: vertical;
  overflow: hidden;
  word-break: break-word;
}
.u-clamp-2 { -webkit-line-clamp: 2; line-clamp: 2; }
.u-clamp-3 { -webkit-line-clamp: 3; line-clamp: 3; }

.u-flex-center {
  display: flex;
  align-items: center;
  justify-content: center;
}

.u-stack-sm, .u-stack-md, .u-stack-lg {
  display: flex;
  flex-direction: column;
}
.u-stack-sm { gap: var(--pn-space-2); }
.u-stack-md { gap: var(--pn-space-4); }
.u-stack-lg { gap: var(--pn-space-6); }

.u-row-sm, .u-row-md, .u-row-lg {
  display: flex;
  flex-direction: row;
  align-items: center;
}
.u-row-sm { gap: var(--pn-space-2); }
.u-row-md { gap: var(--pn-space-4); }
.u-row-lg { gap: var(--pn-space-6); }

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation: none !important;
    transition-duration: 0.01ms !important;
    transition-delay: 0ms !important;
  }
}