You can use styles to format your document so you can quickly and easily apply a set of formatting choices consistently throughout your document. If you want formatting choices that are not available from the built-in styles and themes available in Word, you can modify an existing style and customize it to suit your needs.
Modify an existing style
Right-click a style in the Styles gallery and click Modify.
Make any formatting changes, like new fonts, in the Modify Style dialog box.
For easy access, add your style to the Styles gallery. Check Add to the Styles gallery.
You can also define if the style applies to the current document or to all your documents.