This is a simple CSS trick to customize the size and mouse over property of the blogger Slideshow widget. Go to Blogger -> Template -> Edit Html and look for the below mention code using Ctrl + F.
width: 200px !important;
height: 151px !important;
Add pointer- events: none; as show above to disable the mouse over property on the Slideshow. you can also change the height and width of the Slideshow widget by tweaking the width and height as per your template need.