We can provide styles only for server controls using skin file. But ASP.NET pages are made up of HTML controls, raw HTML or raw Text and to implement style for them we need CSS files within Theme Folder. To create a CSS file for Theme we will click Theme Folder and then select Add New Item. In the list of options we should choose the option Style Sheet and will provide a name say test.CSS. When we are using both skin and CSS file, the skin file will take precedence over CSS file for server controls.