How to use HTML to make a fixed floating translucent search box on the mobile terminal

<!-- 搜索框 -->
<header class="bar">
  <form name="search" class="search" id="search" action="">
    <div class="search-row">
      <input type="search" name="word" id="word">
      <span class="placeholder "><span class="iconfont icon-sousuo"></span><span class="text">搜索</span></span>
    </div>
  </form>
</header>
<!-- 一个背景图 实际上这里往往是轮播图 -->
<div class="background">
  <img src="bg.jpg">
</div>

<style type="text/css">
body {
  margin: 0;  padding: 0;
  font-size: 14px; font-family: "microsoft yahei",&#39;Arial&#39;, &#39;Verdana&#39;,&#39;Helvetica&#39;, sans-serif;
}
.bar {
  position: fixed; top: 0; left: 0; right: 0; /* 决定了搜索框置顶 */
  height: 44px; padding: 0 10px;
  background-color: #fff; opacity: 0.8; /* 搜索框半透明效果 */
  z-index: 10;
}
.bar form {
  display: block; padding: 0;margin: 0;
}
.search-row {
  position: relative;
  height: 30px; padding: 7px 0;
}
.search-row input[type=search] {
  position: absolute; top: 7px;
  height: 30px; line-height: 21px; width: 100%; padding: 10px 15px 10px 30px;
  border: 0; border-radius: 6px; outline: 0; background-color: rgba(0,0,0,0.1);
  font-size: 16px; text-align: center;
  z-index: 100;
}
.search-row .placeholder {
  position: absolute; top: 2px; left: 0; right: 0;
  display: inline-block; height: 34px; line-height: 34px;
  border: 0; border-radius: 6px;
  font-size: 16px; text-align: center; color: #999;
  z-index: 1; 
}
.search-row .placeholder .iconfont {
  display: inline-block; width: 19px; line-height: 24px; padding: 10px 0;
  font-size: 21px; color: #666;
}
.search-row .placeholder .text {
  line-height: 40px;
  vertical-align: top;
}
.background img {
  width: 100%;
}
.active:before {
  position: absolute; top: 11px; left: 5px; right: auto;
  display: block; margin-right: 0;
  font-size: 21px;
}
.active input[type=search] {
  text-align: left
}
.active .placeholder{
  display: none
}
</style>

.active:before {
  position: absolute; top: 11px; left: 5px; right: auto;
  display: block; margin-right: 0;
  font-size: 21px;
}
.active input[type=search] {
  text-align: left
}
.active .placeholder{
  display: none
}
<script type="text/javascript">
/* 输入框获取到焦点 表示用户正在输入 */
$("#word").focusin(function() {
  $(".search-row").addClass("active iconfont icon-sousuo");
});
/* 输入框失去焦点 表示用户输入完毕 */
$("#word").focusout(function() {
  /* 判断用户是否有内容输入 */
  if ($(this).val()=="") {
    /* 没有内容输入 改变样式 */
    $(".search-row").removeClass("active iconfont icon-sousuo");
  } else {
    /* 有内容输入 保持样式 并提交表单 */
    $("#search").submit();
  }
});
</script>