Attach an External Style Sheet in Dreamweaver

Open the CSS Styles Pane if it is not open (will be on the right side).
(to open - Window, CSS Styles)

Lower right corner of that pane....point to the first icon and it will say Attach Style Sheet. Click it to attach.

Some Dreamweaver templates available for purchase on the web use "@import link" for the stylesheet. The import will cause the web page to display first without the help of the stylesheet (very quickly) then show the formatted web page using the stylesheet.

You can solve that by changing the "@import link" for the stylesheet to a direct link. Just remove that line of code, then reattach the stylesheet in Dreamweaver using the method described above.