So here is what I would to for a quick solution. Into your WordPress Customizer, go to “Custom CSS” and add the following:
.tainacan-photoswipe-layer .pswp__bg {
background-color: rgba(255, 255, 255, 0.85);
}
.tainacan-photoswipe-layer .pswp__ui--fit .pswp__top-bar,
.tainacan-photoswipe-layer .pswp__ui--fit .pswp__caption {
background-color: rgba(255, 255, 255, 0.7);
}
.tainacan-photoswipe-layer .pswp__top-bar .pswp__name,
.tainacan-photoswipe-layer .pswp__caption__center {
color: black;
}
.pswp__button, .pswp__button--arrow--left::before,
.pswp__button--arrow--right::before {
filter: invert(100%);
}
.pswp--css_animation .pswp__preloader__donut {
border: 2px solid #000000;
}
Let me now if that is enough