Cartesian-y and .cartesiaon-x classes , position:absolute

why are we using position:absolute on .cartesian-y and .cartesiaon-x classes. I am not able to understand that. I tried removing it and alignment of x and y axis is getting changed. But As I understood from the post, position:absolute should be used along with either top,bottom,left , right keywords. But in the example none of these keywords are used in .cartesian-y or in .cartesian-x css.