post carousel text size style.css

Hi,
First of all thank you for your great apps.
I’m having little troubles to change things in style.css (like always). I want to change the size of the post headings on my post carousel, so i wrote in my style.css :

/* SiteOrigin Carousel */

.sow-carousel-wrapper ul.sow-carousel-items li.sow-carousel-item h3 {
color: #000000;
font-size: 24px;
}

But it doesn’t change anything. What am i doing wrong? is style.css even the place to write that?

URL: http://www.iicp.ch/icp2/ (second Latest News)

Already thank you very much for your help