Use class hide instead of d-none and hidden

app/assets/javascripts/build_variables.js

@@ -4,7 +4,7 @@ export default function handleRevealVariables() {
   $('.js-reveal-variables')
     .off('click')
     .on('click', function click() {
-      $('.js-build-variables').toggleClass('hidden');
+      $('.js-build-variables').toggle('hide');
       $(this).hide();
     });
 }

app/views/projects/jobs/_sidebar.html.haml

@@ -44,7 +44,7 @@
             %p
               %button.btn.group.btn-group.d-flex.js-reveal-variables Reveal Variables
 
-            %dl.js-build-variables.trigger-build-variables.d-none
+            %dl.js-build-variables.trigger-build-variables.hide
               - @build.trigger_variables.each do |trigger_variable|
                 %dt.js-build-variable.trigger-build-variable= trigger_variable[:key]
                 %dd.js-build-value.trigger-build-value= trigger_variable[:value]