flint

If I want the icon to be centered on the page in both desktop on mobile versions what CSS variants need to be changed?Right now with this code:

.scrollup { width: 40px; height: 40px; opacity: 0.9; bottom: 25px; left: px; position: fixed; z-index:100; display: none; background: url('http://static.squarespace.com/static/53e29465e4b09d387c666792/t/541f7527e4b02b592c3dbdfd/1411347751880/scrollarrow.png') no-repeat;}

It appears somewhat centered but slightly off to the right?

When I look at the mobile end my icon is all the way to the left side when on desktop it's on the right hand side anyway to fix the alignment on mobile?