Caption Background Color anfd Font Color

Hello,
I have a metaslider/flexslider as carousell and want to change the background color of the caption. I have tried

.metaslider .caption-wrap {
background: white !important;
color: black !important;
}

but this only works in the firefox inspector, not when implementing it in the custom CSS of my (enfold) theme. Can you help?

Thanks.