Changing format of menu

Hi, On my site, http://dawncavalieri.com the menu is appearing as a dropdown no matter how wide the browser screen is. How can I format it so that the menu items appear across the top and only turn into a drop down when the browser screen is narrow? Can this be done in the Simple Persona theme? Is there something to add to the CSS? Or do I have to change themes? If so, which do you recommend? Thanks.