fix: make donate modal scrollable

[moT01]

I'm not quite sure what you all had in mind for this @raisedadead - but this seems like a quick and easy fix to the scrolling issue - which allows you to get to the close button.

Also, the close button text was underlined - so I got rid of that.

• I have read freeCodeCamp's contribution guidelines.
• My pull request has a descriptive title (not a vague title like Update index.md)
• My pull request targets the master branch of freeCodeCamp.
• None of my changes are plagiarized from another source without proper attribution.
• All the files I changed are in the same world language (for example: only English changes, or only Chinese changes, etc.)
• My changes do not use shortened URLs or affiliate links.

Closes #36756

[gitpod-io]

[raisedadead]

See Ignore previous comments

[raisedadead]

@ahmadabdolsaheb will you be adding the changes like we discussed?

[ahmaxed]

screenshot