[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
[CSS] Add a class to set elements to the full width of their container.
Merge pull request #5066 from thomasgohard/css-full-width

[CSS] Add a class to set elements to the full width of their container
[CSS] Increased border darken to 20% for buttons.
[CSS] Set button borders to 'outset' to give them more depth.
[CSS] Removed the outset border for disabled buttons.