scroll down see background doesn't move

Note that input to the iframe is problematic because the mouse events are eaten
by this content's element. You can fix that with

    pointer-events: none;

but then you get the issue that you can no longer click links nor select text.
You could mark <a> tags as

    pointer-events: auto;

Which would fix links but still no text selection

----

Let's

try

to

make

sure

it's

long

enough

that

we

can

scroll

down

the

page

so

we

can

see

that

position: fixed;

is

a

better

choice

than

position: absolute;

For

a

tall

screen

this

might

take

quite

a

few

lines

of

text

let's

hope

this

is

enough