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.
Click the OK button and this will add a link to the Style sheet that you selected in the Select Style Sheet dialog. Now you can make use of all the styles described in this style sheet.
<link href="StyleSheet.css" rel="stylesheet" type="text/css" />
SDET, Visual Web Developer