how to get values of radio button

hi iam trying to get the values of the radio buttons from this page text and every time i get undefined or
caught TypeError: Cannot read properties of null (reading 'addEventListener')

this is the code i did for now

btn=document.querySelector(".buttonNext");
btn.addEventListener("click", function radio() {
selected=document.querySelector(".css-1crzc9r:checked");
console.log("selected");
});

if it get past to the btn.addeventlisetner i still has the problem of Undefined am i doing something wrong maybe select wrong class or something but i already tried all the classes and they all give me undefined