How Do I Change the Colors on a Theme

Hello! I want to change the colors on the HomePress theme. The background for the slider and the footer are green and the text is white. I want to use Arizona State University colors - maroon and yellow. I tried updating the style sheet but by changing the colors it messed up the layout of the site: no background for the slider and the nice navigation bar turned into a green line instead. The colors didn't change even though all I edited was the colors.