Need to refresh browser before CSS changes are shown

When I make a change to the CSS then run the project, the browser appears to load the styles prior to the changes, like the old version is being cached something?

I already have something in place so I need to log on before the page displays anyway (so at least one postback is made), however I'm still required to click refresh before the new styles are displayed??

Oh, the CSS is stored in the themes folder and I have: <pages styleSheetTheme="default"> set, if that makes any difference.

 

Any ideas would be greatly appreciated.

Thanks.
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