结构:
<form class="demo-a"> <input placeholder="Search" type="search"></form>
关键样式:
.demo-a input{width: 15px; border-radius: 10em; transition: all 0.5s ease 0s;}
.demo-a input:focus{width: 130px; box-shadow: 0 0 5px rgba(109,207,246,.5);}