[#PAB-508]: add scrollable checkboxes

[Joel-Pearce]

Placed the dropdown checkboxes inside a scrollable frame as per ticket: https://trello.com/c/rcDW6WTF/508-adding-ability-to-scroll-in-filters

• Unit tests and other appropriate tests added or updated
• README and other documentation has been updated / added (if needed)
• Commit messages are meaningful and follow good commit message guidelines (e.g. "FS-XXXX: Add margin to nav items preventing overlapping of logo")

[bobbi-hbrown]

The code changes look good from my testing, is there a specific reason for wrapping the checkboxes in a new div rather than attaching the custom CSS to the original govuk-checkboxes? No worries either way I was just wondering :)

[Joel-Pearce]

The code changes look good from my testing, is there a specific reason for wrapping the checkboxes in a new div rather than attaching the custom CSS to the original govuk-checkboxes? No worries either way I was just wondering :)

The class overwrite looked a little more fiddly than just wrapping things in a div (for some of the macros it's not as simples as setting classes='new_class'), if that's what you mean. Might have to do class overwrites for more complicated custom CSS changes though.

[gidsg]

Have we tried adding this class as an additional class on the div below?

[Joel-Pearce]

No, I'll try that, and refactor it if successful.