Update button in _header.html.haml

app/views/admin/application_settings/ci/_header.html.haml

@@ -4,7 +4,7 @@
   = _('Variables')
   = link_to sprite_icon('question-o', css_class: 'gl-vertical-align-baseline!'), help_page_path('ci/variables/README', anchor: 'custom-environment-variables'), target: '_blank', rel: 'noopener noreferrer'
 
-%button.btn.btn-default.js-settings-toggle{ type: 'button' }
+%button.btn.gl-button.btn-default.js-settings-toggle{ type: 'button' }
   = expanded ? _('Collapse') : _('Expand')
 
 %p