Not accessible to keyboard only users

Two quick CSS fixes that could be added here would be:

• adding focus to the hover state as mentioned above;
• adding a default outline on focusable elements set to 1px dotted #000.

I'm happy to help with both today.

I've been working with Denis today and i'll be able to do a follow-up on it.
(Ideally a patch, or at least the exact CSS code suggested.)

Indeed, an outline is needed on focusable elements for accessibility reasons.
It seems that the actual behaviour could be traced back to the use of Eric Meyer's "reset.css", with its recognizable "remember to define focus styles" comment. A quick and precise rationale is available here:
http://www.outlinenone.com/

This could be corrected by replacing this part in "alpha/alpha-reset.css":

/* remember to define focus styles! */
:focus {
  outline: 0;
}

with

:focus {
  outline: 1px dotted #000;
}

Alternatively, on the long term, using normalize.css could be an option, to replace the original reset.css.

Here is what normalize.css offers as best practices for outlines, after thorough experimentation:

/*
 * Addresses outline displayed oddly in Chrome
 */

a:focus {
    outline: thin dotted;
}

/*
 * Improves readability when focused and also mouse hovered in all browsers
 * people.opera.com/patrickl/experiments/keyboard/test
 */

a:hover,
a:active {
    outline: 0;
}

As a themer, I'm not really familiar with patches, but here is what a patch could look like. Please review (using branch 7.x-3,x).

Seems reasonable to me... himerus what do you think of this for a 3.2 inclusion?

Just saw on the 3.2 roadmap. I'll put it as ready to be patched since it's a one liner that won't crash anything

I believe "Needs review" is the correct status, given someone uploaded a patch.