Hello dmcohen!
Follow below steps:
1. Login as admin and go on theme customizer Dashboard — Apperance — Customize or Click on Custimze link on top bar from front-end.
2. Then navigate Additional CSS and put below css into textarea then click on Save & Publish button.
/* Mobile view*/
.panel-image {
height: 25vh;
}
/*Full screen laptop/computer screen view*/
@media screen and (min-width: 48em) {
.panel-image {
height: 25vh;
}
}
Use 25vh for 25% height featured images panel, or you can use 50vh for 50%.
Hope this will helps you.
