Merge branch 'tz-fix-startup-css-sliding-animation' into 'master'

Fixes the sliding problem with startup.css rendering

See merge request gitlab-org/gitlab!39423

app/assets/javascripts/main.js

@@ -156,6 +156,9 @@ function deferredInitialisation() {
   });
 
   loadAwardsHandler();
+
+  // Adding a helper class to activate animations only after all is rendered
+  setTimeout(() => $body.addClass('page-initialised'), 1000);
 }
 
 document.addEventListener('DOMContentLoaded', () => {

app/assets/stylesheets/framework/sidebar.scss

 .content-wrapper {
   width: 100%;
-  transition: padding $sidebar-transition-duration;
 
   .container-fluid {
     padding: 0 $gl-padding;
@@ -13,6 +12,10 @@
   }
 }
 
+.page-initialised  .content-wrapper {
+  transition: padding $sidebar-transition-duration;
+}
+
 .nav-header-btn {
   padding: 10px $gl-sidebar-padding;
   color: inherit;