<script src="https://ajax.googleapis.com/ajax/libs/webfont/1.4.7/webfont.js"></script>
<script>
  WebFont.load({
    google: {
      families: ['Source Sans Pro:300,400,400italic,600', 'Droid Sans Mono']
    }
  });
</script>

<script src="https://ajax.googleapis.com/ajax/libs/webfont/1.4.7/webfont.js"></script>
<script>
  WebFont.load({
    google: {
      families: ['Source Sans Pro:400,400italic,700,700italic', 'Droid Sans Mono']
    }
  });
</script>

Use proper bold fonts instead of this weak semi-bold.
Use proper bold fonts instead of this weak semi-bold.
