%p Kerning
%p.positive.kerning Tomato

%p No kerning
%p.positive.no-kerning Tomato

@import url('https://fonts.googleapis.com/css?family=Source+Sans+Pro:300,400')

html
  font-family: 'Source Sans Pro', 'Open Sans', 'Helvetica Neue', 'Helvetica', sans-serif
  font-kerning: normal
  font-weight: 400
  line-height: 1
  padding: 40px 40px 0

p
  margin: 0 0 10px

.positive
  letter-spacing: 0.125em
  margin-bottom: 20px
  font-size: 45px
  font-weight: 300

.kerning
  // 1. IE will enable kerning only via font-feature-settings.
  font-feature-settings: 'kern'
  font-kerning: normal

.no-kerning
  font-kerning: none