Checkbox trouble

I’m working on the survey project and I’m having issues with the first checkbox in my fieldset. When I add an id the box disappears and I’m not sure why. This is the snippet of code that I’m having issues with:

     <legend>How did you hear about SW Photography? (check all that apply)</legend>
        <input type="checkbox" name="referral" value="facebook-ad" id="facebook-ad"> 
        <label for="facebook-ad">Facebook ad</label>


This doesn’t seem to affect the rest of the page. I copied and pasted this from my code into a new pen and the error seems to be here.

I copied and tested your code on Codepen and it seems to be working fine, what is the issue?

Weird! Maybe its an issue with my browser? This is what I’m getting.

I’m using Chrome and it works fine for me. Try another browser perhaps.