利用的是边框切圆
 <style>
 .box {
 width: 80px; height: 60px;
  margin: 200px;
 padding: 80px 150px;
 position: relative;
 }
 .box div {
 width: 80px; height: 80px;
 border-radius: 50%;
 /*background: blue;*/
 border: 5px solid rgba(255, 255, 255, 0.5);
 position: absolute;
 border-top: 5px solid rgba(255, 255, 255, 1);
 animation: rotate 1.3s infinite;
 }
 @keyframes rotate {
 from { transform: rotate(0deg); }
 to { transform: rotate(360deg);}
 }
 </style>
 </head>
 <body>
 <div class="box">
 <div class="div1"></div>
 </div>
 </body>