[Typo3] How to Get rid of default styles

[Guillaume]

Hello,

Using my own css files for tt_news and newloginbox, I'd like do get rid 
of default css styles in my pages

.....
<style type="text/css"> /*<![CDATA[*/
<!-- /* default styles for extension "tx_newloginbox_pi3" */
...
/* default styles for extension "tt_news" */
...

How can I do that ?

Guillaume