Changing font size to percent in theme I want convert font size in existing theme from px to percentage. The theme and the CSS. Should I change font-size in body and headers only, or better to change font size in all places in CSS? What is the correct way to specify font-size in percent in this particular CSS?

body {
  font-family: 'Open Sans', sans-serif;
  line-height: 160%;
  color: #666;
  font-size:13px;
  background: #fff;
}

h1 {font-size: 18px;}
h2 {font-size: 16px;}
h3 {font-size: 14px;}
h4 {font-size: 13px;}
h5 {font-size: 13px;}
h6 {font-size: 13px;}
This is the perfect place to use em instead of px for your font sizes. Change the font size in your body to font-size: 13px; or something, whatever size you want to be your standard size font.

Then, for all of the other elements, you can use em to adjust the size of the font based on percent. For example, font-size: 1.5 em; would be 1.5x larger than the standard size of 13px, and font-size: 0.5 em; would be 0.5x the size of the standard of 13px;