If necessary, regenerate permalinks in order to display the archive of the Contributors
As you want, copy the file style.css in custom-style.css (same directory) and set your rules of style
As you want, create in your theme directory the single.php in single-contributorpost.php
As you want, create in your theme directory the archive.php in archive-contributorpost.php
Go to 'Contributors Posts Settings' -> 'Generale Settings' and configure HTML for your theme
Go to 'Contributors Posts Settings' -> 'Customize Contributor, Category and Tag Setting' and configure which post_type associate contributors,
where show contributors posts, and if activate special plugin page for show contributor post and archive.