Header tags and em Sass function

[cshold]

• Added a function to convert pixel font sizes to em automatically
  • @mpiotrowicz, used a slight variation of the one you pointed me to. Uses em(20px) rather than just em(20)
  • I think it makes it a bit more clear to understand what is happening with the unit attached
• Cleaned up use of h1 and h2 page title tags (as per recent comment on Schema article #90)
• Minor cleaning of padding/margins to use gutter rather than ems

@jholl @stevebosworth

[mpiotrowicz]

works for me!