Closes #456 (closed)
Added css for outlines in the styles.scss file. You can change the color of the outline there. Not sure, where the blue in the picture comes from, might be your browser, since I dont have it.
I would suggest using on-surface as the color, because this gives us the AAA-tested color contrasts for the frame. However, there is no contrast requirement for outlines in the WCAG, so if you prefer to use another color for better visuals, we could do that, too.
I noticed some inconsistencies with the tab behaviour on the imprint page, that I will adress in another issue.