How do I change the styles and layout of blocks on pages?
You can easily style up your wiki aspects by following this tutorial https://www.xwiki.org/xwiki/bin/view/Documentation/DevGuide/Tutorials/SkinExtensionsTutorial/#HMinimalStyleSheetextension.
where i can change html code?
No, you don’t understand. How do I change the right block in all pages?
From that, as was mentioned above, you can use Skin with your customization.
@hookeym for the left/right block of the page, you actually refer to the page panels and all the details about panels you can find in https://extensions.xwiki.org/xwiki/bin/view/Extension/Panels%20Application.