Left offset property

HTML-CSS
1

https://learn.freecodecamp.org/responsive-web-design/applied-visual-design/create-movement-using-css-animation

I’m having hard time even to start with this, what is horizontal and how to set the left offset?

3

skewY: left; it would be the answer?

5

left offset property are 0 pixels at 0%, 25 pixels at 50% and -25 pixels at 100%. change it to px dont use the %