/* ==========================================================================
   研究项目集
   极简 · 平色 · 无渐变无阴影 · 方砖式卡片
   ========================================================================== */

:root {
  /* 乐高亮蓝作为界面主色，方向颜色由数据注入 --tile-color */
  --blue:       #0055bf;
  --blue-press: #003f91;
  --blue-soft:  #e6efff;

  --ink:   #14161a;
  --ink-2: #5b6472;
  --ink-3: #949cab;

  --bg:   #f4f5f7;
  --card: #ffffff;
  --line: #e4e7ec;

  --tile-color: var(--blue);

  --r-s:  10px;
  --r:    16px;
  --r-l:  20px;

  --wrap: 1080px;
}

* { box-sizing: border-box; }
[hidden] { display: none !important; }

body {
  margin: 0;
  background: var(--bg);
  color: var(--ink);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", "PingFang SC",
               "Hiragino Sans GB", "Microsoft YaHei", Helvetica, Arial, sans-serif;
  font-size: 15px;
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
}

h1, h2 { margin: 0; line-height: 1.15; letter-spacing: -.03em; font-weight: 800; }
p { margin: 0; }
a { color: inherit; text-decoration: none; }
img { display: block; max-width: 100%; }
button, input { font: inherit; color: inherit; }
svg { display: block; }

.wrap { max-width: var(--wrap); margin: 0 auto; padding: 0 22px; }

:focus-visible { outline: 3px solid var(--blue); outline-offset: 2px; border-radius: 6px; }

.skip-link { position: absolute; left: -9999px; }
.skip-link:focus { left: 12px; top: 12px; z-index: 10; background: var(--ink); color: #fff; padding: 8px 14px; border-radius: var(--r-s); }

/* ---------------------------------------------------------------- 顶部栏 -- */

.topbar { background: var(--card); border-bottom: 1px solid var(--line); }
.topbar-inner { display: flex; align-items: center; justify-content: space-between; height: 60px; gap: 16px; }

.brand { display: flex; align-items: center; gap: 10px; }
.brand-mark {
  width: 28px; height: 28px; flex: none; border-radius: 8px;
  background: var(--blue); display: grid; place-items: center;
}
.brand-mark svg { width: 16px; height: 16px; }
.brand b { font-size: 15.5px; font-weight: 700; letter-spacing: -.01em; }

.topbar-links { display: flex; gap: 18px; font-size: 14px; color: var(--ink-2); }
.topbar-links a:hover { color: var(--blue); }
.topbar-links:empty { display: none; }

/* ------------------------------------------------------------------ 首屏 -- */

.hero { padding: 66px 0 30px; }
.hero h1 { font-size: clamp(30px, 5.4vw, 46px); }
.hero-sub { margin-top: 14px; font-size: 16px; color: var(--ink-2); max-width: 30em; }
.hero-count { margin-top: 8px; font-size: 13.5px; color: var(--ink-3); }

/* ---------------------------------------------------------------- 搜索框 -- */

.searchbar {
  display: flex; align-items: center; gap: 10px;
  max-width: 460px; margin-top: 26px;
  background: var(--card); border: 2px solid var(--line); border-radius: 999px;
  padding: 0 8px 0 18px; height: 50px;
  transition: border-color .15s;
}
.searchbar:focus-within { border-color: var(--blue); }
.searchbar svg { width: 18px; height: 18px; flex: none; color: var(--ink-3); }
.searchbar:focus-within svg { color: var(--blue); }
.searchbar input { flex: 1; min-width: 0; border: 0; background: none; outline: none; padding: 0; }
.searchbar input::placeholder { color: var(--ink-3); }
.searchbar input::-webkit-search-cancel-button { display: none; }
.searchbar-clear {
  flex: none; width: 32px; height: 32px; border: 0; border-radius: 50%;
  background: var(--bg); color: var(--ink-2); cursor: pointer;
  font-size: 17px; line-height: 1; display: grid; place-items: center;
}
.searchbar-clear:hover { background: var(--blue-soft); color: var(--blue); }

/* ---------------------------------------------------------------- 类目 -- */

.filters { padding: 30px 0 0; }
.chips { display: flex; flex-wrap: wrap; gap: 8px; }
.chip {
  display: inline-flex; align-items: center; gap: 6px; cursor: pointer;
  height: 38px; padding: 0 16px; border-radius: 999px;
  background: var(--card); border: 1px solid var(--line); color: var(--ink);
  font-size: 14px; font-weight: 500;
  transition: border-color .15s, background .15s, color .15s, transform .1s;
}
.chip em { font-style: normal; font-size: 12px; color: var(--ink-3); }
.chip .dot { width: 9px; height: 9px; border-radius: 50%; flex: none; }
.chip:hover { border-color: var(--blue); color: var(--blue); }
.chip:hover em { color: var(--blue); }
.chip:active { transform: scale(.97); }
/* 选中态的背景色由 JS 按方向颜色写入行内样式 */
.chip[aria-selected="true"] em { color: currentColor; opacity: .65; }

/* ------------------------------------------------------------------ 网格 -- */

.grid {
  display: grid; gap: 20px; padding: 26px 0 0;
  grid-template-columns: repeat(auto-fill, minmax(236px, 1fr));
}

.tile {
  display: flex; flex-direction: column; overflow: hidden;
  background: var(--card); border: 1px solid var(--line); border-radius: var(--r-l);
  transition: transform .16s, border-color .16s;
}
.tile:hover { transform: translateY(-3px); border-color: var(--tile-color); }
.tile:active { transform: translateY(-1px); }

.tile-media { aspect-ratio: 4 / 3; background: var(--blue-soft); position: relative; }
.tile-media img { width: 100%; height: 100%; object-fit: cover; }
.tile-ext {
  position: absolute; top: 10px; right: 10px;
  width: 24px; height: 24px; border-radius: 50%;
  background: #fff; color: var(--tile-color); font-size: 12px;
  display: grid; place-items: center;
}

.tile-body { padding: 14px 16px 17px; display: flex; flex-direction: column; gap: 5px; }
.tile-cat { font-size: 11.5px; color: var(--ink-3); letter-spacing: .03em; }
.tile-title { font-size: 16px; font-weight: 700; letter-spacing: -.015em; }
.tile-desc {
  font-size: 13.5px; color: var(--ink-2); line-height: 1.55;
  display: -webkit-box; -webkit-line-clamp: 2; -webkit-box-orient: vertical; overflow: hidden;
}
.tile mark { background: #cfe0ff; color: inherit; border-radius: 3px; }

/* 占位砖：项目少时补齐一行，版面不空 */
.tile-ghost {
  border: 1px dashed #d3d8e0; background: none;
  display: grid; place-items: center; min-height: 220px; padding: 24px;
  text-align: center; color: var(--ink-3); font-size: 13px;
}
.tile-ghost:hover { transform: none; border-color: #d3d8e0; }
.tile-ghost span { display: block; }
.tile-ghost .plus {
  width: 34px; height: 34px; margin: 0 auto 10px; border-radius: 10px;
  background: var(--bg); color: var(--ink-3);
  display: grid; place-items: center; font-size: 19px; line-height: 1;
}

/* ------------------------------------------------------------- 空结果 -- */

.empty { padding: 70px 0 40px; text-align: center; }
.empty p { color: var(--ink-2); }
.empty .btn { margin-top: 18px; }

.btn {
  display: inline-flex; align-items: center; cursor: pointer;
  height: 42px; padding: 0 22px; border-radius: 999px;
  border: 1px solid var(--blue); background: var(--blue); color: #fff;
  font-size: 14.5px; font-weight: 600;
  transition: background .15s, transform .1s;
}
.btn:hover { background: var(--blue-press); border-color: var(--blue-press); }
.btn:active { transform: scale(.97); }

/* ------------------------------------------------------------------ 页脚 -- */

.footer { margin-top: 76px; border-top: 1px solid var(--line); background: var(--card); }
.footer-inner {
  display: flex; flex-wrap: wrap; gap: 10px 20px;
  align-items: center; justify-content: space-between;
  padding: 22px 0; font-size: 13px; color: var(--ink-3);
}
.footer-links { display: flex; gap: 16px; }
.footer-links a:hover { color: var(--blue); }

/* ---------------------------------------------------------------- 响应式 -- */

@media (max-width: 620px) {
  .wrap { padding: 0 16px; }
  .hero { padding: 42px 0 22px; }
  .searchbar { max-width: none; }
  .grid { grid-template-columns: repeat(2, 1fr); gap: 14px; }
  .tile-body { padding: 12px 13px 15px; }
  .tile-title { font-size: 14.5px; }
  .tile-desc { -webkit-line-clamp: 3; font-size: 12.5px; }
  .tile-ghost { display: none; }
  .chips { overflow-x: auto; flex-wrap: nowrap; padding-bottom: 4px; scrollbar-width: none; }
  .chips::-webkit-scrollbar { display: none; }
  .chip { flex: none; }
}

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