[e.cash] Prevent social icons in nav from flashing

Summary: Social icons are flashing for a sec on load on desktop. Adding some CSS to avoid

Test Plan: preview the site and check you dont see the icons

Reviewers: #bitcoin_abc, bytesofman

Reviewed By: #bitcoin_abc, bytesofman

Subscribers: bytesofman

Differential Revision: https://reviews.bitcoinabc.org/D16639