Dropdown menu full height and alignment issues

Hi there, 

I can't find a CSS code that makes my dropdown menu full height on the page. Right now the menu is only a small square but I would like it to go to the top of the page and completely down. Similar to this website https://www.tiffanyleighdesign.com/home

This is what my menu currently looks like.I also need a code to make the dropdown options aligned with the menu above. Any help is appreciated!