Difficulty with image clarity in Explore template

We are having difficulty making images appear clearly in 4 buttons on the home page of the Explore theme. I've included a link to our website below under private information.

Specifically, it's the images on the home page behind DIY INSPIRATION (paint brushes), GARDENING (pink flower), CRAFTS (paper crafts), HOLIDAYS (balloons).

We've tried increasing the file size, changing the file type (.jpg, .png), removing background overlays, but the images still appear fuzzy when viewed on the front side of the website. They are nice and crisp in the media library and otherwise.

Thanks for any assistance in helping us resolve this issue.