Regarding the site changing is just me swapping CSS-theme, because I tried to located if the 'error' was outside the CSS-file or inside til CSS-file.
BUT - I've found out that, as you wrote - it all is in the CSS-file.
Somehow, because of me working directly on the 'live' CSS-file via Cyberduck and CSSEdit, there was created a lot of new invisible CSS-files everytime i saved it in CSSEdit - So my corrections didn't reflect in the correct CSS-file (style.css) but was saved in the invisible style-1.css, style-2.css etc.)
So now it ought to work - but thanks for all the advice.