Putting elements on top of side wrappers?

How do one put elements (like images) inside left and/or right sidewrapper? Good guess is it is done by stylesheets but how?

How to make them float sticky and not to move along with the rest of a page when scrolling up and down?

How do one put elements (like images) inside left and/or right sidewrapper?
You attach/insert an image to the particular container and insure that the backgroung color for it is transparent
For what you referenced it could be either of these -
#navColumnOne or .columnLeft

There is nothing with stylesheets that is ZenCart only and a source for learning could be http://www.w3.org/Style/

Yes, after editing tpl_index_default.php and adding image urls there I can get images to index pages side wrappers but what should I do if I wanted them to be displayed with every single page? Is there any "master" php for that?

Yes, **after editing tpl_index_default.php **and adding image urls there I can get images to index pages side wrappers but what should I do if I wanted them to be displayed with every single page? Is there any "master" php for that?
Not at all what I referenced...

If you look at the classic template stylesheet.css file, and search for the term "background" - - You will see how an image is applied

Not through a php file edit

How to make them float sticky and not to move along with the rest of a page when scrolling up and down?

You can use position: fixed; to make an element stay in the same window location and not scroll. I'm not sure that would work well for sidebar backgrounds, though.