Hi Sue,
Unfortunately, there is not a declarative way to change the styling of the radio buttons themselves. The appearance of the buttons actually varies depending on what type of browser you are using. I noticed a difference in my buttons when using Chrome vs. Firefox. Please see this article explaining that without using custom JavaScript libraries or images, the style of radio buttons are determined by the browser.
https://stackoverflow.com/questions/4253920/how-do-i-change-the-color-of-radio-buttons
