Was going to suggest tips but Chris said exactly what I would do. First and foremost Ctrl+F5 to refresh the browser. Then I would use Firebug to see if the changes are being made or if your CSS attributes are being overridden / inherited. What I would do is that I would not work on directly modifying the CSS file of minimal extropy but rather I would have my own CSS file and then load it from the ascx file via a rel statement. In that way you would have any changes in the same place and would not lose the original CSS attributes (or at least comment them out). Try putting a drastic change in the CSS file such as body {background-color:red;}. In this way you would surely notice if the CSS is being refreshed / loaded.

I am having the same issue, making me crazy = ( There must be some kind of time setting in the server cache.