Background Color Hover Fade Effect CSS

First, I am a beginner. I want a step by step instruction.

I want to add a smooth background hover effect to my links in Wordpress

a {
  color:#000;}
a:hover {
  background-color: #d1d1d1; color:#fff;
}

I want the hover on links slow, instead of instant. Do I need any JavaScript or jQuery ? If so, please tell me how to do that.