Refactor the "clear / X" button

[teolemon]

Originally posted by @teolemon in #4232 (comment)

[g123k]

Why not, but why is the cross button using rounded corners, whereas the plus doesn't?
And also, why isn't the plus icon not circled also?

[teolemon]

@monsieurtanuki @g123k
The positioning is not right. I was wondering whether we could overlay it above the card, on the very top right, with some of it outside the card.
This would free up a lot of real estate to do a better layout within the card (eg more text, more visuals…)