message: backTop demo
diff: return(<div id="components-back-top-demo-custom-2">
  <BackTop target={() => document.querySelector('.content').parentNode} />
  Scroll down to see the bottom-right
  - <strong style={{ color: 'rgba(64, 64, 64, 0.6)' }}> gray </strong>
  + <strong> original </strong>
  button.
  </div>)
  }
  @@ -35,39 +35,39 @@ render(){
  <div className="fishd-back-top-inner">UP</div>
  </BackTop>
  <p>Scroll down to see the bottom-right
  - <strong style={{ color: '#1088e9' }}> blue </strong>
  + <strong style={{ color: '#1088e9' }}> UP </strong>
  button.
  </p>
  <p>Scroll down to see the bottom-right
  - <strong style={{ color: '#1088e9' }}> blue </strong>
  + <strong style={{ color: '#1088e9' }}> UP </strong>
  button.
  </p>
  <p>Scroll down to see the bottom-right
  - <strong style={{ color: '#1088e9' }}> blue </strong>
  + <strong style={{ color: '#1088e9' }}> UP </strong>
  button.
  </p>
  <p>Scroll down to see the bottom-right
  - <strong style={{ color: '#1088e9' }}> blue </strong>
  + <strong style={{ color: '#1088e9' }}> UP </strong>
  button.
  </p>
  <p>Scroll down to see the bottom-right
  - <strong style={{ color: '#1088e9' }}> blue </strong>
  + <strong style={{ color: '#1088e9' }}> UP </strong>
  button.
  </p>
  <p>Scroll down to see the bottom-right
  - <strong style={{ color: '#1088e9' }}> blue </strong>
  + <strong style={{ color: '#1088e9' }}> UP </strong>
  button.
  </p>
  <p>Scroll down to see the bottom-right
  - <strong style={{ color: '#1088e9' }}> blue </strong>
  + <strong style={{ color: '#1088e9' }}> UP </strong>
  button.
  </p>
  <p>Scroll down to see the bottom-right
  - <strong style={{ color: '#1088e9' }}> blue </strong>
  + <strong style={{ color: '#1088e9' }}> UP </strong>
  button.
  </p>
  <p>Scroll down to see the bottom-right
  - <strong style={{ color: '#1088e9' }}> blue </strong>
  + <strong style={{ color: '#1088e9' }}> UP </strong>
  button.
  </p>
  </div>
  