Styled Textarea is a simple customizable textarea editor for Umbraco. With Styled Textarea, you can define three attributes on the textarea element in your editor. You can define how many rows you want the editor to span, you can add classes for styling, and you can add inline styles.
All for the benefit of your editors.
Pick Styled Textarea as the editor, when creating a new datatype. Fill in the blanks, and voila.