HTML/CSS Assessment questions about the 600px

Hi guys,
I have some questions regarding these 4 bullet points:

  • … is 600px wide when the screen is greater than or equal to 600px wide
  • … uses grid layout to layout labels and form elements when the screen is greater than or equal to 600px wide
  • … is the width of the screen when the screen is less than 600px wide
  • … lays out the labels and form elements as full width when the screen is less than 600px wide

I was wondering if someone can take a look at what I have so far and see if I am on the right track.
I am having some issues formatting when the screen is less than 600px.