Learn how to create alert messages with CSS.
Read on how to do it in this link: https://www.w3schools.com/howto/howto_js_alert.asp
Alerts
Alert messages can be used to notify the user about something special: danger, success, information or warning.
Try it yourself here: https://www.w3schools.com/howto/tryit.asp?filename=tryhow_js_alert
Tip: Also check out Notes.