image.png

index.html

  1. <body>
  2.   <div class="search-index"></div>
  3. </body>

index.css

.search-index {
  position: fixed;
  top: 0;
  left: 50%;
  transform: translateX(-50%);
  /* 固定定位的盒子应该有宽度 */
  width: 100%;
  height: 44px;
  min-width: 320px;
  max-width: 540px;
  background-color: blue;
}