如何使用css修改滚动条默认样式的代码实例

<p class="inner">
 <p class="innerbox">
 <p style="height:200px;">这是内容111</p>
 <p style="height:400px;">这里是内容222</p>
 <p>这里是内容333</p>
 </p></p>

　　　　.inner{
 width: 265px;
 height: 400px;
 position: absolute;
 top: 33px;
 left: 13px; 
 /*cursor: pointer;*/
 overflow:hidden;
 }
 .innerbox{
 overflow-x: hidden;
 overflow-y: auto;
 color: #000;
 font-size: .7rem;
 font-family: "\5FAE\8F6F\96C5\9ED1",Helvetica,"黑体",Arial,Tahoma;
 height: 100%;
 } /*滚动条样式*/
 .innerbox::-webkit-scrollbar {/*滚动条整体样式*/
 width: 4px; /*高宽分别对应横竖滚动条的尺寸*/
 height: 4px;
 }
 .innerbox::-webkit-scrollbar-thumb {/*滚动条里面小方块*/
 border-radius: 5px;
 -webkit-box-shadow: inset 0 0 5px rgba(0,0,0,0.2);
 background: rgba(0,0,0,0.2);
 }
 .innerbox::-webkit-scrollbar-track {/*滚动条里面轨道*/
 -webkit-box-shadow: inset 0 0 5px rgba(0,0,0,0.2);
 border-radius: 0;
 background: rgba(0,0,0,0.1);
 }