[e.cash] Switch theme

Summary: Teeing up the stealth mode switch

Test Plan: preview the site and it should be in stealth mode. Check everything looks good and functions normally

Reviewers: #bitcoin_abc, bytesofman, Mengerian

Reviewed By: #bitcoin_abc, bytesofman, Mengerian

Subscribers: Mengerian, Klakurka, bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D14343