Merge branch 'small-flash-ux-improvement' into 'master'

Use 0.15s transition duration for flash close

See merge request gitlab-org/gitlab!24830

app/assets/javascripts/flash.js

@@ -11,7 +11,7 @@ const FLASH_TYPES = {
 const hideFlash = (flashEl, fadeTransition = true) => {
   if (fadeTransition) {
     Object.assign(flashEl.style, {
-      transition: 'opacity .3s',
+      transition: 'opacity 0.15s',
       opacity: '0',
     });
   }

spec/javascripts/flash_spec.js

@@ -40,7 +40,7 @@ describe('Flash', () => {
 
       expect(el.style['transition-property']).toBe('opacity');
 
-      expect(el.style['transition-duration']).toBe('0.3s');
+      expect(el.style['transition-duration']).toBe('0.15s');
     });
 
     it('sets opacity style', () => {