To make the required input, the element must be an input element. Change your buttons to the inputs, give them a name, add the required one and change the type to "radio", and the required one should work ( see this script ):
<div> <input type="radio" name="radio-choice" required>Admin</input> <input type="radio" name="radio-choice" required>User</input> </div>
Unfortunately, this means that they no longer look like cool buttons. You can stylize the radio buttons so that they look the way you want, and the required one will still prevent the form from being submitted, but you will not see a pop-up warning to select an option ( see This script ).
So, for what you want, it looks like you will need to do some basic programming. Here's a fiddle with basic validation using the original buttons.
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