17720/17721 invalid project link in timelines table and cut off modal close icon

https://community.openproject.org/work_packages/17720
https://community.openproject.org/work_packages/17721
@ulferts I realise naming the stylesheet folder _legacy_ might have been ambiguous, because _legacy_ could mean:

1. styles for legacy (i.e. server-side Rails/non-Angular) components and views 
2. legacy stylesheets - a whole load of different styles added over the years in an ad-hoc fashion (and that used to be part of `main.css`)

What I actually meant though was no. 2.

It was my intention that we do gradual cleanup/refactoring. I'd like to get to a point where we can delete the entire `app/assets/stylesheets/legacy` folder.

If we need to add _new_ styles for Rails/non-Angular components, views, then `app/assets/stylesheets/content` is the right place for this – albeit perhaps with an appropriate comment. In some cases, it might also be appropriate to apply _legacy_ to class names (as I did in 038d32f5, for example).