Import theme variables into popup styles (#299)

Author: DiogoRibeiro7

_sass/minimal-mistakes/vendor/magnific-popup/_magnific-popup.scss

@@ -1,5 +1,7 @@
 /* Magnific Popup CSS */
 @use 'sass:math';
+// Import theme variables so popup fonts match the site
+@use "../../variables" as *;
 @use "settings" as *;
 
 ////////////////////////

_sass/minimal-mistakes/vendor/magnific-popup/_settings.scss

@@ -1,5 +1,8 @@
 @use 'sass:math';
-@use "minimal-mistakes/variables" as *;
+
+// Import theme variables so popup styles use the same fonts and colours.
+@use "../../variables" as *;
+
 ////////////////////////
 //      Settings      //
 ////////////////////////