Applying Styles in Fill Format Mode
From LibreOffice Help
You can quickly apply styles, such as paragraph and character styles, in your document by using the Fill Format Mode in the Styles and Formatting window.
- Choose View - Styles and Formatting.
- Click the icon of the style category that you want to apply.
- Click the style, and then click the Fill Format Mode icon
- Move the mouse pointer to where you want to apply the style in the document, and click. To apply the style to more than one item, drag to select the items, and then release.