Deleting Overlay Caption in Tempera Theme

Hello,

I want to make two changes to the image captions in Tempera Theme:

1. Change background-color of the overlay caption. Currently background color is black.
2. Place the caption below the picture instead of on the image i.e. I want to delete overlay caption

Here is the link where you can see the images with overlay captions that have black background.

Could anyone help?

Thanks