Slash (/) vs tilde slash (~/) in style sheet path
/- Site root~/- Root directory of the application
The difference is that if you site is:
http://example.comAnd you have an application myapp on:
http://example.com/mydir/myapp/ will return the root of the site (http://example.com),
~/ will return the root of the application (http://example.com/mydir/).
The second won't work because its not a recognised path by anything except asp.net code on the server side. And since your link tag is regular html and not a server control it never gets processed.
If you add runat="server" in your link tag then it would works perfectly....
like this....
<link href="~/common/black_theme/css/style.css" rel="stylesheet" runat="server"> (this is also working)