Revise Tailwind configuration and styling

Currently, [default Nuxt Ignis CSS file](https://nuxt-ignis.netlify.app/3-2-features-ui.html#default-css-file) is disabled in settings and https://github.com/AloisSeckar/ELRHistory/blob/main/app/assets/css/tailwind.css is in effect. This should be rewised and highly customized contents from `tailwind.css` eliminated as much as possible...