Let's say I imported a theme into my forum and would like to change the color of certain parts of the theme (for example, change the background of the header from black to blue, or change the color of certain texts) - where shall I start with? Thanks!
please read first:
https://docs.mybb.com/1.8/development/themes/
some styles have different color schemes
ACP --> Themes --> Your Theme --> Scroll down to "Manage Colors"
if there is nothing, you will have to edit global.css or other css
With F12 in your browser you can check, which part you will have to change