[Glitch] Fix prev/next buttons color in media viewer

Port 675672feb6 to glitch-soc

Signed-off-by: Claire <claire.github-309c@sitedethib.com>

app/javascript/flavours/glitch/styles/components/media.scss

@@ -236,7 +236,7 @@
   background: transparent;
   box-sizing: border-box;
   border: 0;
-  color: rgba($primary-text-color, 0.7);
+  color: rgba($white, 0.7);
   cursor: pointer;
   display: flex;
   align-items: center;
@@ -251,7 +251,7 @@
   &:hover,
   &:focus,
   &:active {
-    color: $primary-text-color;
+    color: $white;
   }
 }