This would probably be complicated to include as a theme feature. However, with some basic HTML and CSS knowledge, this is easy to achieve in the HTML editor.
<span style="background: #eee;">Your sentence here.</span>
will produce a sentence with a light grey background.
If you prefer to use the visual editor, you can use a child theme to create shortcodes to do this, or use one of the many plugins that will create shortcodes for you.