Add toggleable transparency option

[PylotLight]

• Update all styling to vars
• Add optional transparency option
• Will look to add configurable styling presets/color picker later

Note:

• I'm no design specialist but the Codex transparency thing does look more modern I think, but plenty room for improvement still.
• Also I annoyingly included all the items from the other PR in this branch due to a rebase I needed to do, I'm sure we can split out the changes if needed.

[vercel]

@PylotLight is attempting to deploy a commit to the dev Team on Vercel.

A member of the Team first needs to authorize it.