Allow for custom overrides by the user

_sass/overrides.scss

@@ -0,0 +1,3 @@
+//
+// Custom overrides from a user.
+//

assets/css/just-the-docs.scss

@@ -42,3 +42,4 @@
 @import "./tables";
 @import "./code";
 @import "./utilities/utilities";
+@import "./overrides";