Styles Heading 1, Heading 2, and Heading 3 are often used by search engines to extract relevant information from html pages. These heading styles should be used for outlining the information in the text, not for formatting.
Users have the option to set their browser to a style other than the default.
If you want the text to be outlined and appear in a certain way, you need to apply the heading outline style and a special format style. Type a few words, highlight them and change to bold and italics.