Main menu not displayed horizontally, etc.

Testing this theme on a clean install with some test content, there are some problems: The Main menu, when placed in the Menu region, is not displayed horizontally, but instead displayed as a raw HTML list, with the menu labels stack vertically. Also, the background is white and does not match the rest of the page. Lastly, the attached screenshot shows how the fields in the user login block are breaking out of the block.