Hiding headers and footers on pages

Hello, thank you for all your help so far, we are very happy. A little while agi you gave me this code below to hide headers and footers on pages. I added to additional css in theme options but it does not work. Just red “X” errors show. Can I just copy and paste this or do I need more code to make it work?

//checkout page
.page-id-13802 #masthead .masthead{
display:none;
}
//hide footer checkout page
.page-id-13802 .wrapper-footer{
display:none;
}

//cart page
.page-id-13800 #masthead .masthead{
display:none;
}
//hide footer cart page
.page-id-13800 .wrapper-footer{
display:none;
}