I use notepad to edit the style sheet directly. Then I refresh the page and validated the stylesheet still in old status. (use F12 browser developer tool to validate)
In the Master page I added "v=1" or "v=10" or "v=whatever" like below:
<SharePoint:CssRegistration name="/_layouts/mycompany/styles/OverallStyles.css?v=2" runat="server" after="SharepointCssFile" />
However the page still not load the updated CSS. I have also tried ctrl+F5 to reload but no help. What should I do?