<form method="post" name="ice_cream" id="ice_cream" action="https://cs12.net/form/submit.php">
   <fieldset>
     <legend>Would you like ice cream?     </legend>
     <label>
       <input type="radio" name="want" id="ic_yes" value="yes"/>
Yes     </label>
     <label>
       <input type="radio" name="want" id="ic_no" value="no"/>
No     </label>   </fieldset>
   <fieldset id="icecream_options">
     <legend>Ice Cream Options     </legend>
     <fieldset>
       <legend>Would you like a cup or a cone?       </legend>
       <label>
         <input type="radio" id="container_cup" name="container" value="cup"/>
Cup       </label>
       <label>
         <input type="radio" id="container_cone" name="container" value="cone"/>
Cone       </label>     </fieldset>
     <fieldset>
       <legend>What topping do you want?       </legend>
       <label>
         <input type="checkbox" name="toppings" id="toppings_wc" value="whipcream"/>
Whipped cream       </label>
       <label>
         <input type="checkbox" name="toppings" id="toppings_jimmies" value="jimmies"/>
Jimmies       </label>
       <label>
         <input type="checkbox" name="toppings" id="toppings_sprinkles" value="sprinkles"/>
Sprinkles       </label>
       <label>
         <input type="checkbox" name="toppings" id="toppings_nuts" value="nuts"/>
Nuts       </label>
       <label>
         <input type="checkbox" name="toppings" id="toppings_cherry" value="cherry"/>
Cherry       </label>     </fieldset>   </fieldset>
   <button type="submit">Submit Order   </button>
 </form>  

In style element (<style>) within head element:

label {
  display: block;
}

input[type=submit],
button[type=submit] {
  display: block;
}
form fieldset {
  margin-bottom: 1rem;
}
#icecream_options {
  border-style: none;
}
button.clicked {
  border: 3px solid purple;
}
ul.resourcelist {
  border: 2px solid black;
  border-radius: 5px;
}
.hidden {
  display: none;
}
body {
  font-family: helvetica, sans-serif;
  margin: 1rem;
  line-height: 1.5;
}

In script element within head element (<script>):

document.addEventListener('DOMContentLoaded',function(){
    console.log("dom is loaded!");
    let iceCreamOptions = document.querySelector('#icecream_options');

    iceCreamOptions.classList.add("hidden");
    let wantRadioInputs = document.querySelectorAll("form input[name=want]");

    wantRadioInputs.forEach(function(el){
        console.log(el);
        el.addEventListener("click",function(){
            console.log("radio button was just clicked!");
            let yesRadio = document.querySelector('#ic_yes');
            if (yesRadio.checked == true) {
                console.log("Yes is checked!");
                iceCreamOptions.classList.remove("hidden");
            } else {
                console.log("Yes is NOT checked");
                iceCreamOptions.classList.add("hidden");
            }
        })
    });

});