@MojtabaMosavi
Posted
If you already haven't read the css tricks guide for grid I recomend it. Quite detailed and easy to grasp.
1- The why us section could also be seen a list of item which is more meaningful semantically rather that just a div.
2- Add some kind of hover state to your button to make is more interactive, the least accepeted is change of cursor which communicates to the user that this element is interactive.
Keep coding :=)