https://makandracards.com/makandra/1402-vim-scroll-up-down-keeping-your-cursor-in-its-row
C+E : scroll-up.
C+Y : scroll-down.
C+U : Move viewport Up.
C+D : Move viewport Down.
zz, z. : middle
z, zt : top.
z-, zb : bottom.
:w !sudo tee %.