[e.cash] Language selector CSS

Summary:
Adding some overrides and a new hover effect on the language selector styles

It is a rectangle now on the live site, but it should be a square. The padding values coming from weglot changed at some point

Test Plan: Can only test live due to weglot setup, but the selector will be a square again with these css edits

Reviewers: #bitcoin_abc, Fabien

Reviewed By: #bitcoin_abc, Fabien

Subscribers: Fabien

Differential Revision: https://reviews.bitcoinabc.org/D14631