[CSS] Updated the overrides for the visited link color.
[CSS] Moved the font scaling ratios to variables so that they can be reused to scale other things.
[CSS] Scaled the top margins for the headings using the font scale ratios.
Merge pull request #5063 from thomasgohard/css-visited-links

[CSS] Updated the overrides for the visited link color
Merge pull request #5064 from thomasgohard/css-heading-margins

[CSS] Updated heading margins to increase readability