.header{
  position: relative;
}
.header-input{
  margin:22rpx 36rpx 14rpx 34rpx;
  height:72rpx;
  border: 1rpx solid #D9DDE1;
  border-radius: 36px;
  padding:0 36rpx;
  font-size: 26rpx;
  text-align: center;
}
.header-input-placeholder{
  color: rgba(133,133,133,0.60);
}
.header-input-icon{
  position:absolute;
  left:50%;
  top:18rpx;
  transform: translateX(-189rpx);
  color: rgba(133,133,133,0.60);
}

​<!--index.wxml-->
<view class="header">
  <input
    type="text" 
    class="header-input" 
    placeholder="AngularJS·MySQL·Java"
    placeholder-class ="header-input-placeholder"/>
    <icon type="search" class="header-input-icon" size="18"></icon>
</view>