remove subcategories thumbnail images from shop page

I have been scanning the internet for more than 4 hours in an effort to hide the subcategory thumbnail images (not the name of the subcategory just the image) from the shop page.

I have selected the option from the appearance>customise to show the subcategories on the shop page but i only want to display their names not their photos.
I have tried CSS codes but it unfortunately also removes the category thumbnail images as well.
Can someone please help?
Ideally i would like to show the subcategory title with a background colour and no image thumbnail in the shop page.