Open an existing web site in VWD. Open the page by double clicking on it in solution explorer to which you want to attach the existing style sheet in your web site. Now, switch to Design View of the page and bring up Select Style Sheet dialog by clicking on menu: Format –> Attach Style Sheet as shown below
See the original post here:
Tip #68 Did you know… How simple it is to attach an existing style sheet to your web page?