Sorry, there is not currently any way to change that behavior.
Those default css classes for the controls are important for presenting a consistent look and feel for all your portlets.
If you want to change the rules of those css classes for your entire site, you can customize those css rules in your skin.
Or if you just want a custom look only for your specific portlet (or page), you can provide your own css stylesheet that override the rules of the default css classes with ones that have a higher specificity.
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