EhUI v3

Changelog

• Themes use CSS custom properties instead of SASS/SCSS variables
• Seperate CSS file(s) for themes and the rest of ehui's styles, instead of one giant CSS file for each theme.
• Better hover/focus colors, especially for textboxes
• New button-boxes
• Styles for details element/tag
• Better .button.alt styling
• Better combo-select styles
• Seperate searchbar styles
• Removed .screen class
• Added .thin-centered, which replaces hacky usage of .screen class (like in Quizfreely's sign-in page)
• Better, more organized, folder structure with src, build, and site
• Documentation mabye
• Rewrote SVGs to use background, and be in each seperate theme css file, using the same sass function
• Use partial syntax/naming-convention in scss filenames
• Adjust themes again again