Here's how you will make your blogspot (former blogger) Header fixed so all of your Blog contect will scroll under the Header (exactly like you can see it here).
Do a backup of your Template first then Login to your Blog-account and go to Design >> EDIT HTML (checkmark expand Widgets)
and then Search for: .header-outer {
when found add this:
overflow:hidden;
position:fixed;
z-index:999999;
width: 1440px;
That's it :) Please leave a comment ;)