Hello Eva,
I didn’t make any changes in the styles. I only removed the Newsletter static block from the single product sidebar (in the widget area). But this had the bad effect that the brand as well as the upsell products disappeared as well. So I created an empty static block (called: Nix) and placed it in the single product sidebar (in the widget are). This made the brand and upsell products appear again, but the empty “Nix” widget creates some white space to the TAB description area.
My initial issue was to move the TAB description area as close as possible toward the upper area.
Kind regards!