The extension creates valid (X)HTML and is styled with CSS. You can reset my default style with the following code in your page's template:
plugin.tx_smemployeelist_pi1._CSS_DEFAULT_STYLE >
plugin.tx_smemployeelist_pi2._CSS_DEFAULT_STYLE >
You can take my CSS definitions from the files pi1/static/setup.txt and pi2/static/setup.txt in the extension's folder, add it to a custom stylesheet and change it the way you like.