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<!DOCTYPE html>
<html>
<script src="https://ajax.googleapis.com/ajax/libs/angularjs/1.6.9/angular.min.js"></script>  
<style>
input.ng-invalid {
    background-color:pink;
}
input.ng-valid {
    background-color:lightgreen;
}
</style>
<body ng-app="">
<p>Try writing in the input field:</p>
<input ng-model="myName" required>
<p>The input field requires content, and will therefore become green when you write in it.</p>
</body>
</html>