Magento 1.9 - How to add if - else condition in CSS?

I just want to change font behaviour based on the website, how to add if - else condition in css.

My CSS :

td.email-heading h1 {
  font-weight: 700;
  font-size: 16px;
  margin: 1em 0;
  line-height: 20px;
  text-transform: uppercase;
}

If website 1 font-weight: 700 should work, if website 2 should not work.