/* ─────────────────────────────────────────
   功能页通用「返回上一页」按钮
   - 图标化、无文字：不再用大胶囊占版面
   - 玻璃质感：适配各页深色渐变头部（靛蓝 / 青绿 / 赭红 / 深黑）
   - 回上一页（history.back），不硬跳首页；没有可返回的历史时由 JS 隐藏
   ───────────────────────────────────────── */
.page-back {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  width: 38px;
  height: 38px;
  padding: 0;
  border: 1px solid rgba(255, 255, 255, .34);
  border-radius: 50%;
  background: rgba(255, 255, 255, .16);
  color: #fff;
  cursor: pointer;
  -webkit-tap-highlight-color: transparent;
  -webkit-backdrop-filter: blur(6px);
  backdrop-filter: blur(6px);
  transition: background .18s, border-color .18s, transform .18s;
}
.page-back:hover { background: rgba(255, 255, 255, .28); border-color: rgba(255, 255, 255, .52); }
.page-back:active { transform: scale(.94); }
.page-back:focus-visible { outline: 2px solid rgba(255, 255, 255, .85); outline-offset: 2px; }
.page-back svg { display: block; }
.page-back[hidden] { display: none; }

/* 视频页顶栏更暗，底再压一点，避免糊成一块 */
.vf-topbar .page-back { background: rgba(255, 255, 255, .12); border-color: rgba(255, 255, 255, .28); }