Add new style guides created into existing style guidelines (admin dashboard)

[daaimah123]

See open issue: #505 to detail where and how to document updates to style for the site.

This sub-issue is asking someone to ensure that the new proposed style implementations specific to the admin dashboard are documented if they are introducing style conventions that the website has not yet used or documenting.

Merge into mvp branch.

[daaimah123]

Potential to be blocked by completion of Create basic administrator dashboard with dummy overview statistics