Good Morning Jeffrey,
It is possible to change the background color. In this snippet that you added to your custom CSS:
.boxcaption {
color: #000;
background: #fff;
background: rgba(255, 255, 255, 0.8);
}
The last line background: rgba(255, 255, 255, 0.8);
controls the background color. You can replace the rgba(255, 255, 255, 0.8) with another RGBA color. There is an online one at https://developer.mozilla.org/en-US/docs/Web/CSS/Tools/ColorPicker_Tool that you can use to find the right color.
The first three number, 255, 255, and 255 in our example set the hue. The last number 0.8 sets the opacity on a scale of 0 (transparent) to 1.0 (completely opaque).
While it is possible to set the captions to center align, the alignment will only stick for part of the caption. I’m not entirely certain why, but it looks like you’ll have to stick with the text left aligned.
Take care,
Bill