Function to Check Sub Page Existence

I am working on developing a custom theme, and I would like help with finding a code snippet or writing a custom function that will or will not display a bit of CSS depending upon whether the current page has subpages or same level pages. In other words, I would like this style applied if the current page is either a parent with subpages or if the parent of the page has subpages. Any suggestions on how to do this would be greatly appreciated. Thank you much in advance.