.alg-difficulty-badge {
  display: inline-block;
  padding: 1px 8px;
  border-radius: 4px;
  font-size: 12px;
  font-weight: 700;
  margin-right: 8px;
  vertical-align: middle;
}
.alg-difficulty-简单 { background: #e8f5e9; color: #2e7d32; }
.alg-difficulty-中等 { background: #fff3e0; color: #e65100; }
.alg-difficulty-困难 { background: #ffebee; color: #c62828; }

.alg-category-tag {
  display: inline-block;
  padding: 0 6px;
  margin: 2px;
  background: #f0f0f0;
  border-radius: 3px;
  font-size: 11px;
  color: #666;
}

.alg-source { font-size: 13px; color: #888; margin-right: 8px; }
.alg-source-link { font-size: 12px; color: var(--color-link); }
.alg-label { font-size: 12px; color: #999; margin-right: 4px; }
.alg-label + .alg-label { margin-left: 12px; }
.alg-complexity { font-size: 12px; margin-right: 12px; }

.alg-tag {
  display: inline-block;
  padding: 0 6px;
  margin: 2px;
  background: #e3f2fd;
  border-radius: 3px;
  font-size: 11px;
  color: #1565c0;
}

.alg-info-card {
  border: 1px solid #e0e0e0;
  border-radius: 8px;
  padding: 12px 16px;
  margin: 16px 0;
  background: #fafafa;
}
.alg-info-row { margin: 6px 0; }

@media (prefers-color-scheme: dark) {
  .alg-difficulty-简单 { background: #1b5e20; color: #a5d6a7; }
  .alg-difficulty-中等 { background: #e65100; color: #ffcc80; }
  .alg-difficulty-困难 { background: #b71c1c; color: #ef9a9a; }
  .alg-category-tag { background: #333; color: #ccc; }
  .alg-tag { background: #1a237e; color: #90caf9; }
  .alg-info-card { border-color: #444; background: #2d2d2d; }
  .alg-source { color: #aaa; }
  .alg-label { color: #888; }
}
.category-tree { list-style: none; padding: 0; margin: 0; }
.category-tree-item { margin: 4px 0; }
.category-tree-item.has-children.collapsed > .tree-children { display: none; }
.tree-toggle { cursor: pointer; font-size: 10px; margin-right: 4px; user-select: none; color: #999; }
.tree-toggle:hover { color: var(--color-link); }
.tree-children { list-style: none; padding-left: 18px; margin: 2px 0 4px; }
.tree-children .category-list-link { font-size: 13px; }
@media (prefers-color-scheme: dark) {
  .tree-toggle { color: #888; }
}

/* Top nav dropdown (纯CSS hover，fade-up动效，与侧边栏AOS风格统一) */
.nav-dropdown { position: relative; }
.nav-dropdown-menu {
  position: absolute;
  top: 100%;
  left: 50%;
  transform: translateX(-50%) translateY(8px);
  min-width: 140px;
  background: var(--color-wrap);
  border-radius: 10px;
  padding: 6px 0;
  z-index: 1000;
  list-style: none;
  margin: 8px 0 0;
  box-shadow: 0 0 10px 3px var(--color-hover-shadow);
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  transition: opacity 0.3s ease, transform 0.3s ease, visibility 0.3s;
}
.nav-dropdown:hover > .nav-dropdown-menu,
.nav-dropdown-menu:hover {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
  transform: translateX(-50%) translateY(0);
}
/* 悬停桥接 */
.nav-dropdown-menu::before {
  content: "";
  position: absolute;
  top: -8px;
  left: 0;
  right: 0;
  height: 8px;
}
.nav-dropdown-menu li { position: relative; margin: 0; }
.nav-dropdown-menu li a {
  display: block;
  padding: 8px 20px;
  color: var(--red-0);
  opacity: 0.7;
  text-decoration: none;
  font-size: 14px;
  font-weight: 700;
  letter-spacing: 1px;
  white-space: nowrap;
  transition: 0.3s;
}
.nav-dropdown-menu li a:hover {
  opacity: 1;
  color: #fff;
  background: var(--red-1);
}
.nav-dropdown-menu li:first-child a:hover { border-radius: 10px 10px 0 0; }
.nav-dropdown-menu li:last-child a:hover { border-radius: 0 0 10px 10px; }
.nav-dropdown-menu li:only-child a:hover { border-radius: 10px; }

/* 三级菜单 */
.nav-dropdown-submenu {
  position: absolute;
  top: -6px;
  left: 100%;
  min-width: 100px;
  background: var(--color-wrap);
  border-radius: 10px;
  padding: 6px 0;
  list-style: none;
  margin: 0 0 0 4px;
  box-shadow: 0 0 10px 3px var(--color-hover-shadow);
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  transform: translateY(4px);
  transition: opacity 0.3s ease, transform 0.3s ease, visibility 0.3s;
}
.nav-dropdown-sub:hover > .nav-dropdown-submenu,
.nav-dropdown-submenu:hover {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
  transform: translateY(0);
}
.nav-dropdown-submenu li { margin: 0; }
.nav-dropdown-submenu li a {
  display: block;
  padding: 8px 20px;
  color: var(--red-0);
  opacity: 0.7;
  text-decoration: none;
  font-size: 14px;
  font-weight: 700;
  letter-spacing: 1px;
  white-space: nowrap;
  transition: 0.3s;
}
.nav-dropdown-submenu li a:hover {
  opacity: 1;
  color: #fff;
  background: var(--red-1);
}
.nav-dropdown-submenu li:first-child a:hover { border-radius: 10px 10px 0 0; }
.nav-dropdown-submenu li:last-child a:hover { border-radius: 0 0 10px 10px; }
.nav-dropdown-submenu li:only-child a:hover { border-radius: 10px; }

/* ===== Search Popup (from theme search.scss, unconditionally included) ===== */
.popup {
  visibility: hidden;
  position: fixed;
  top: 10%;
  left: 50%;
  width: 700px;
  max-height: 80%;
  margin-left: -350px;
  padding: 3px 0 0 10px;
  background: var(--color-wrap);
  color: var(--grey-9);
  z-index: 9999;
  border-radius: 10px;
  opacity: 0;
  transform: scale(0.5);
  transition: 0.3s;
  box-shadow: 0 0 10px var(--color-meta-shadow);
}
.popup.show {
  visibility: visible;
  opacity: 1;
  transform: scale(1);
}
@media screen and (max-width: 767px) {
  .popup {
    padding: 5px;
    top: 0;
    left: 0;
    margin: 0;
    width: 100%;
    height: 100%;
    border-radius: 0;
    max-height: 100%;
  }
}
.reimu-popup {
  overflow: hidden;
  padding: 0;
}
.popup-btn-close {
  color: var(--red-1);
  font: 20px bold;
  padding-left: 15px;
  transition: 0.3s;
}
.popup-btn-close:hover {
  opacity: 0.8;
}
.reimu-search {
  display: flex;
  align-items: center;
  padding: 8px 15px;
  max-height: 50px;
  border-bottom: 1px solid #ccc;
  border-radius: 5px 5px 0 0;
}
.reimu-search-input-icon {
  display: inline-block;
  width: 20px;
  font-size: 18px;
  vertical-align: middle;
  margin-right: 5px;
}
.reimu-search-input {
  flex: 1;
}
.reimu-search-input input {
  width: 100%;
  outline: none;
  border: none;
  background: transparent;
  color: var(--grey-9);
  font-size: 16px;
  vertical-align: middle;
  font-family: "Noto Serif SC", "Source Han Serif SC", "Noto Serif CJK SC", "Source Han Serif CN", serif, "Noto Sans", "Helvetica Neue", Helvetica, Arial, "PingFang SC", "Microsoft YaHei", sans-serif;
}
.reimu-results {
  position: relative;
  overflow: auto;
  padding: 15px 30px;
  box-sizing: border-box;
  max-height: calc(100% - 50px);
}
@media screen and (min-width: 768px) {
  .reimu-results {
    min-height: 300px;
  }
}
.reimu-results hr {
  margin: 10px 0;
}
.reimu-results em {
  font-weight: bold;
  margin: 0;
  padding: 0 2px;
  color: var(--red-1);
}
#reimu-hits {
  margin: 10px 0 0 10px;
}
#reimu-hits mark {
  background: var(--red-1);
  color: white;
}
.reimu-hit-item-link {
  display: block;
  text-decoration: none;
  color: var(--red-2);
  padding: 12px 0 12px 25px;
  white-space: nowrap;
  text-overflow: ellipsis;
  overflow: hidden;
}
.reimu-hit-item-link:before {
  content: "";
  width: 6px;
  height: 12px;
  background: var(--color-h2-after);
  display: inline-block;
  vertical-align: middle;
  margin: -2px 11px 0 -25px;
  box-shadow: 0 2px 12px var(--color-red-6-shadow);
  opacity: 0.5;
  transition: 0.2s;
}
.reimu-hit-item-link:hover:before {
  height: 6px;
  border-radius: 50%;
  opacity: 1;
}
.reimu-hit-item {
  list-style: none;
}
.search-result-cats {
  font-size: 13px;
  color: var(--grey-9);
  margin-left: 25px;
}