CSS for a button

I created a child theme for my site, tdotargetmarketing.com. If you look, you'll see the header has three buttons. I broke the header down to the table you see below. Slice 3, 5 and 7 are the buttons on the site that need to be clickable. I created pages for those three buttons so I have the url/page. I added this table below in the editor section of the childtheme's css file. Now, I think I need to go to the Themes Option and scroll down to the Custom Css and add #header {} with the url/page location but this is where I'm stuck. Not sure of the proper sequence. Don't laugh, lol... I just finished the HTML/CSS basic course on Codecademy so I'm getting it but just not quite there. Can anyone help with this?