Cannot change JQueryUI theme

I am using the extension quickdlgs with Yii 1.1.15 to display a message.

Everything is working as long as I use the default theme.

Now I want to use a different theme in one view of my project.

After downloading the theme from I saved all the files in a folder "/css/overcast" in my project folder.

echo EQuickDlgs::contentButton(array(








Why does this code not display the dialog using the CSS of the downloaded theme?

Please help!