buttontobutton

This might not the right forum, but would appreciate any thoughts. In my codepen I am animating a div with an image in it. The issue is that I am animating my div left from 100% to -100%. However -100% is WAY longer than when the rightmost edge of the div is off of the screen, adding extra time. I essentially want it to end up at right: 100%. Is there a way using CSS to get it to stop at the equivalent of right: 100%, but while animating left? I was able to solve the issue by calculating the values dynamically on window.resize and killing and redeclaring the tween. Surely there has to be a better way? Thank you.