CodePudding user response：

The code seems to work correctly when I check it in Device Tool Bar of Chrome. Try it in dev tools(f12). Chrome documentation : https://developer.chrome.com/docs/devtools/device-mode/

Latest browsers don't go less than 500px in width when you try to make the window smaller. That is the reason why you dont see blue in your video. If you still want to try using the browser width, try changing 480px to 600px. You will be able to see the Media Queries working then.