.o-footer,
.o-footer a:not(.a-btn) {
  color: #fff;
}
.img-sources-expander .img-sources-expander__details .img-sources-expander__summary:before {
  background-image: url(
https://www.einstiegbahnbau.de/resource/crblob/13431354/107905598598a7113b16ba707d15bf78/fix_footer_white-arrow-data.svg
);
}