Change styles of date selector modal

[rcantin-w]

Off the back of #10234 and a chat with @j-jaworski , we decided to split that piece of work for that section as it would probably require a redesign/rethink of that area.

Using the placeholder as a label doesn't work as it disappears once focused, but adding a label the same way we'll do the other input fields doesn't quite work either.

Feel free to move this back to the backlog, but as it's kind of part of the raised accessibility issue that was #10234 I'm starting it off in Next for now?

[j-jaworski]

I think this should be covered by the design proposal for events in search Design MVP for events in search#10569

Link to designs in Figma https://www.figma.com/file/e6Nng9zRjZITtYAZHpF1dB/Events-%26-Exhibitions-in-Search?type=design&node-id=117%3A1814&mode=dev&t=y3d1d0OvliFtIqBB-1

[pollecuttn]

Size: small