Hi … changing the styling of the text components of the Biography Box is done by your site’s theme and not by the plugin. The HTML for the Biography Box that the plugin emits has rudimentary CSS to ensure the relationship between the avatar and the biography text works and to style to list that contains the contact links, but everything else inherits from the CSS that your theme uses.
If you want to change what your theme uses for presentation styling then the best course would be to create a custom CSS file which overrides the part of your theme’s CSS which you want to change and which affects only the Biography Box. See this post – https://www.vicchi.org/codeage/wp-biographia/hacking-wp-biographias-appearance-with-css/ – for background information on how to do this.
So if you want to change the CSS for the Biography Box’s title, you’d override .wp-biographia-text h3, if you want to override the CSS for the biography text itself, you’d override .wp-biographia-text p and if you want to override the CSS for the contact links, you’d override .wp-biographia-links small … and so on.
-Gary
