Improve accessibility with keyboard navigation
That "the website is usable for users who use a keyboard and not a mouse" is the second requirement on Digitaliseringsstyrelsens list on web accessibility.
Web Accessibility
Include everyone. Respect the law on Web Accessibility. Be careful with content and structure. Regularly perform WCAG tests.
Mark external links and PDF files with CSS
It's a boost to the usability of your website when you clearly indicate that a link leads out of the site or to a PDF file.