Question

I am looking at the theme eleven40 from studiopress.

When I shorten the browser window a lot (being a mobile responsive theme), the logo goes to 100% width making the menu fall beautifully under.

Any idea how this is done?

Answer 1

This is CSS3 media queries. Check for example this article on CSS Tricks.

In this particular case next rule does the job:

@media only screen and (max-width: 800px) {
    ...
    #title {
        width: 100%;
        padding: 18px 0 17px;
    }
    ...
}