[Enhance] cleanup all theme logic and styles

[gbowne1]

I noticed that;

• we now have a theme.js

This should house all theme related things from all files.

The current files that have any theme logic and or style are:

theme.js L# all
main.js L# 300-310
login.html L# 220-230
styles.css L# 40-50
index.html L# 90-100
manifest.json L# 90-100
register.html L# 220-230
theme.test.js L# all

Consider using variables for theme including light and dark mode

Ensure that the PWA theme color on all pages match. Noted as a meta tag theme-color.

[gbowne1]

#111 #99 should fix this