Show invalid or valid icon in form input field

The following demo will show the icon in the form input field when it's valid or invalid:

<style>
input:required:invalid {
  background-image: url(data:image/png;base64,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);
  background-position: right top;
  background-repeat: no-repeat;
  box-shadow: none;
}

input:required:valid {
  background-image: url(data:image/png;base64,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);
  background-position: right top;
  background-repeat: no-repeat;
}
</style>


<form name="testForm">
    <input type="text" name="firstname" required="required" minlength="3" maxlength="10" pattern="^[a-zA-Z ]+$" />
    <input type="text" name="lastname" required="required" minlength="3" maxlength="10" pattern="^[a-zA-Z ]+$" />
</form>