Adjust footer for mobile

I created a footer at this

URL https://sarahpharrisphotography.net/preciousmemories/ it works find when you view on the computer

#footer_copyright {

float: left;
width: 1423px;
background-color:#000000;
color: #50c3c4;
}

but it’s too long when I view it via mobile.. How to fix it for a mobile version