The script was also imrpoved so that the button for the selected stylesheet was disabled, so it couldn't be clicked again.
var themeCss = ['default.css','high.css','plain.css','olden.css'];
var themeName = ['Default','High Contrast','Plain','Olden'];
var themeId = "themeSwitch";
The gist I wrote about the switcher on GitHub, has been update to include these latest changes. Probably it can be simplified and generalised even further.