Why does an entire paragraph change when I try to change a title style?

This happens when your title is included in the code for the paragraph it precedes. The Show Blocks tool in the Mura CMS toolbar will reveal formatting issues.

Click the Show Blocks icon  to see what text is included within a paragraph. The image below shows Title 1 included within paragraph code whereas Title 2 is its own entity and can be styled separtely from the paragraph below.  To separate Title 1 from the paragraph with which iit is grouped, place your cursor after the last letter of the title (in this case the number one) and hit Enter on your keyboard. This action is also called a hard return. Now your title is wrapped in its own paragraph box and can be styled accordingly.