Open the text element for editing and select the portion of text for which you want to apply a Style. If you want to apply the Style to all the text, you can use the shortcut key Control+A, or Command+A on Mac.
Select the bottom portion of the Styles button from the Home tab.
Select the desired Style from the list.
Note: If you apply Styles to individual portions of a text element and then decide you'd like to apply a different Style to the entire element, only the portions of text with no previous Styles applied will be changed. This allows you to use certain Styles on some text to add emphasis and another Style to the remainder of your text without having to select the multiple fragments between the previously styled portions. If you'd like the portions with previous Styles applied to be changed also, you will need to remove the other Styles first by de-selecting the Style from the pulldown list on the Styles button.
Note: Applying a style to a portion of a list will apply to the style to the entire list. You cannot have different styles applied to parts of the same list.
Note: If the Style will not apply to your text, try selecting the text and then clicking the Remove HTML Markup button and/or Clear All Formatting button from the Paragraph section of the Home tab then repeat the steps above.