Tryit Editor v2.7

Edit This Code:

<!DOCTYPE html>
<html>
<script src="http://ajax.googleapis.bootcss.com/ajax/libs/angularjs/1.4.8/angular.min.js"></script>  
<style>
textarea.ng-invalid {
    background-color:pink;
}
textarea.ng-valid {
    background-color:lightgreen;
}
</style>
<body ng-app="">

<p>Try writing in the textarea field:</p>

<textarea ng-model="myName" required>

The textarea requires content, and will therefore become green when you write in it.