Twenty Thirteen: How to remove gray box around DIVs?

Hi All:

I have a site in progress using the twenty thirteen theme, + holi child theme, here: http://www.radionowhere.net/sandbox .

The navbar text links to anchors in the same page. When these nav links are clicked on twice (not once, oddly, the anchor divs are surrounded by an ugly gray box (this is in both Chrome and Safari on Mac).

I assumed this had something to do with a:visited or a:active CSS code somewhere in the theme, but haven’t been able to eradicate the box. Anyone have an idea as to what might be causing this?

Thanks for your help!