Using your web browser's development tools, find the ID of the image slider (Photo Gallery Element in slideshow view):
Use the code below as a template and replace the ID (cc-m-13596341525) with yours:
<style type="text/css">
/* full width image slider */
#cc-m-13596341525 {
width: 100vw;
left: calc(-50vw + 50%);
position: relative;
padding: 0px;
}
.cc-m-gallery-slider ul img {
height: auto !important;
}
</style>
For best results, use images that are at least 1500 pixels wide and make sure all images have the same dimensions.