If you're applying styles or formatting to your text using the editor but your content isn't reflecting those changes, there may be some hidden styles in the source of your content.
Hidden styles often make their way into content it is copied and pasted from another source like a web page or word processing program. To get rid of any hidden formatting, you'll need to remove or 'clear' these styles from your content.
Highlight the area you are experiencing issues with and click the "remove styles" icon as shown. This will reset the text back to its default style and you can use the built in editor style buttons to reformat the text as you wish.