Slider – image not displaying

I created a new page and added a image in featured image and in customization -> slider -> added this new page
The image was displayed in the slider but in mobile version a white text box always appeared in the bottom, I thought if I change it colour to match image it will become invisible.
So I tried to change all colour setting because of which the image disappeared. It think it is because I changed the background overlay colour. Could anyone help me set it back to transparent so that the image becomes visible again.

The page I need help with: [log in to see the link]