Codex Theme Header cut off on Mobile Site

Using the Codex theme; the header on the desktop website is perfect, displaying the full header image as well as the header text, which is either the title of the blog when on the homepage or the title of the blog post when on that post’s page. Yet when on a mobile device, half of the header is cut off while the article itself is fully visible. How can I fix this? And I do not know how to code so if I could fix this using the WordPress features, that would be great!

The page I need help with: [log in to see the link]