How can I set CSS using javascript (I don't have access to the CSS file)?

#fade div {

  -webkit-transition: opacity 1s;

  -moz-transition: opacity 1s;

  -o-transition: opacity 1s;

  -ms-transition: opacity 1s;       

  transition: opacity 1s;

  opacity: 0;

  position: absolute;

  height: 500px;

  width: 960px;

}

For example:

document.getElementById('fade').HOW-TO-TYPE-webkit-transition = 'opacity 1s';