Sticky header shortcode not working

[alextokyoesque]

I've been trying to make the header for the website www.tokyoesque.com freeze in place so that it is still visible and clickable when scrolling down, but the code I have tried has shifted some text on the homepage to an undesirable position. Can anyone help me find a way to get the sticky header to work without messing up the position of other elements of the page? The code I have tried is as so: /Sticky header/ header#masthead { position: fixed; width: 100%; z-index: 100; }