please increase the contrast of different sections in apps
What kind of contrast would you be talking about more specifically? There are some things that Zorin can handle, and other things are either up to Gnome, or up to the application developers themselves.
If you give a few examples, it might be possible that we could find a solution as well, as there are some ways to get high contrast, depending on the situation.
for an example, the type boxes are sometimes indistinguishable. like the type boxes found when I'm changing the password of my computer and Vivaldi browser's search/web address box..
When it comes to vivaldi, they would probably have to look into doing something on their end if it's a popup for their program. As for Zorin dialogue boxes, as startreker has mentioned, it might be worth trying out high contrast in the Accessibility settings and see if that might help out a bit.