Form controls can be grouped by using the fieldset element. A fielset can also include a legend element to caption the enclosed fields.
<fieldset>
<legend>Pizza specs</legend>
<fieldset>
<legend>Crust (choose one)</legend>
...
</fieldset>
<fieldset>
<legend>Toppings (choose as many as you want)</legend>
...
</fieldset>
</fieldset>