"Wonky" CSS / layout when header and sidebar are removed

Here’s the reason it looks weird, then we’ll give the fix:

Salesforce’s standard header styles, which are added to the page when you have Show Header turned ON, add the following lines of CSS to the page, which make the page not look “wonky”:

body {
   font-size: 75%;
}

a {
   color: #333435;
}


So if you add this CSS into your pages where you have Show Header OFF, they should look more normal.