In which template can Outer border Width be set for posts view?
 

I need help, i know this is too dumb to ask, but i have since i can't find the solution by myself.

I need info where i can add padding for "posts view" left and right, since atm the padding is 0 - but only in "posts/thread view", in "forum view" (and announcements...) the value for padding is correct and can be defined from All Style Options > Outer Border Width (pixels).

Which template must i edit to correct this?

Try this, go to your Styles Manager click Style Vars on the drop down for that theme, and write down your Sizes & Dimensions settings. Now click the revert boxes beside those you've changed and save.

Now try changing them again as needed. You might find you've got one set wrong.

If you want to poke around your templates, try the SHOWTHREAD template. If you open that template and search it for the word tag, you'll find the area that's in your 2nd image.
(You'll also find the variables that are called from the Style Vars mentioned above)

If that template is edited, you might want to revert it to see if that solves the prob.

HTH