The Default Theme does not have the proper CSS and will default to a stacked theme. Have you tried any of the other Advanced (A) themes that have built-in side-by side layout options?
My guess is your WordPress theme is not wide enough to fit two 400px wide sections plus their necessary margins before auto-wrapping the content. You may want to start with a smaller size for each of the div CSS rules.
You may also need to create an outside wrapper div with a new CSS style that sets position:relative; display: block; width:100%; for the style rules. Something like div id=’map_wrapper’ and a css rule #map_wrapper may help.
Creating HTML and CSS rules inside WordPress themes that do not conflict with all the things the theme styles do can be a challenge. It is one of the primary drivers behind creating more Advanced Themes that have a variety of settings. It is a pain to select an advanced theme, apply, save, test multiple times but it is far easier than hacking custom HTML & CSS to get things to look right. Eventually I’d like to pair SLP themes to WP themes and even start creating basic WP themes designed with SLP components built-in.