I am pretty sure PhotoSwipe has not fonts of its own – it inherits from your theme. You should be able to change it using custom CSS (from your WP dashboard, under Appearance → Customize → Additional CSS). If you provide me with a link, I can tell you how.
I am using the wpastra theme.
At this moment on a local virtual machine. So I can not give you a link.
I can install it on a hosted environment tomorrow and send you a link then.
Regards,
Hans
Solved, added the css below :
/* color and textsize for gallery caption bottom*/
.title-display-slideup-stick a .photonic-title {
font-size: 1em;
color: whitesmoke ;
}
/* text color and size in photoswipe */
.pswp * {
color: red;
font-size: 18px;
}
/* color and textsize for gallery caption below */
a.photonic-lb.photonic-photoswipe.photoswipe {
text-decoration: none;
color:black;
text-align: center;
font-size: 1.2em;
}