ACTION-298: Greater visibility for keyboard focus

From Kevin White:

This is relevant for links and form elements.
Suggestion: For all elements that have a :hover styling, add in a :focus styling as well. For example, style.css line 860 has:
.main-nav a:hover span {
color: #5e6266;
}
Simply add:
.main-nav a:hover span, .main-nav a:focus span {
color: #5e6266;
}
It is noted that there is some specific :focus styling, but this does not appear to be functioning, and there is little reason to make this different from the :hover styling.