There are HTML syntax/coding errors you should be aware of and address.
Since copy/paste from codepen you can ignore the first warning and first two errors.
Codepen provides validators for HTML, CSS and JS. Click on the chevron in the upper right of each section and then click on the respective ‘Analyze’ link.
The one for CSS is good. Use it and address the issue(s). (be wary of creating duplicate selectors as it can make maintenance a nightmare)
(The one for HTML misses things which is why I recommend W3C)
User’s should be able to click on the label to toggle a selection, not just the radio button / checkbox (this is not working with your checkboxes)
It’s a bad UX if the user has to delete text from the textarea in order to enter their comments
Pretty much everything that Roma said is useful, I have one little suggestion though if you’ll re-visit that webpage again.
Try using a :hover selector for the submit button. Here’s an example that I did:
#submit:hover {
background-color: #7dba2f; /*Same outline color that you used for border-color*/
transition: background-color 0.2s; /*transition to that background-color within 0.2 seconds*/
}