.required:after { content:" *"; color: red; }

 

<label class="required">Name:</label>
<input type="text">

<style>
  .required:after {
    content:" *";
    color: red;
  }
</style>

https://stackoverflow.com/questions/11197671/use-css-to-automatically-add-required-field-asterisk-to-form-inputs