css refactor

[epertt]

• removed unused css classes
• added many css variables
• used css variables whenever possible
• reordered style.css; variables first, most used classes second, less used classes third, identifiers fourth, media queries last
• reworked some parts to make more sense from a technical viewpoint
• probably many other minor things i forgot

not directly related to css, but whatever:

• moved task change buttons to where the task buttons are
• moved pupu speech bubble up slightly