ant-design/components/back-top/demo/custom.md

order	title
1	[{zh-CN 自定义样式} {en-US Custom style}]

zh-CN

可以自定义回到顶部按钮的样式，限制宽高：40px * 40px。

en-US

You can customize the style of the button, just note the size limit: no more than 40px * 40px.

import { BackTop } from 'antd';

ReactDOM.render(
  <div>
    <BackTop>
      <div className="ant-back-top-inner">UP</div>
    </BackTop>
    Scroll down to see the bottom right <strong>blue</strong> button.
  </div>,
  mountNode
);

#components-back-top-demo-custom .ant-back-top {
  bottom: 100px;
}
#components-back-top-demo-custom .ant-back-top-inner {
  height: 40px;
  width: 40px;
  line-height: 40px;
  border-radius: 4px;
  background-color: #57c5f7;
  color: #fff;
  text-align: center;
  font-size: 20px;
}