Resolve "Fix loaders in dark theme"

changes/changelog.d/1442.bugfix

+Fixed minor graphical bug where loaders would appear white in dark theme (#1442)

front/src/style/_main.scss

@@ -47,6 +47,7 @@ $bottom-player-height: 4rem;
 @import "./components/_track_table.scss";
 @import "./components/_user_link.scss";
 @import "./components/_volume_control.scss";
+@import "./components/_loaders.scss";
 
 @import "./pages/_about.scss";
 @import "./pages/_admin_account_detail.scss";

front/src/style/components/_loaders.scss

+.ui.dimmer {
+  background-color: var(--dimmer-background);
+}
+
+.ui.loading.form:before {
+  background-color: var(--dimmer-background);
+}