How do I center?

As you can see here, the ‘center’ value isn’t a property of float.

To center a slideshow, make sure you’ve given it a fixed width that’s smaller than the containing page’s width. You can set the width in the slideshow’s setting ‘Width of the slideshow’.

After setting the slideshow’s width, set the slideshow’s style to ‘Custom’. A custom style editor will open up, in which you need to do the following:

.slideshow_container {
        margin: 0 auto; /* Add this line to center the slideshow */
}