Accessibility: Links do not have a discernible name for buttons

[AdamPS]

For more background see Drupal issue #3263821.

When using Lighthouse in the Chrome Developer Tools to test a page that shows a few buttons (Email, Twitter, and Facebook), the Accessibility test returns this warning for the buttons:

"Links do not have a discernible name."

I believe this is because on mobile, when the buttons are small, no text is shown, so the link "has no name."

[AdamPS]

Currently when the buttons are small, the button text is entirely missing (display: none). If instead we make the button text visually hidden, then the problem will be solved.