Take rows & cols input from the user. ( Will give you idea of handling inputs )
Handle onFocus & onBlur events to highlight selected cell.
1->A , 2->B , 3 ->C, 4 ->D ...... 26 -> Z, 27 -> AA, 28 -> AB ...... 52 -> AZ, 53 -> BA
PS: Do not sought help of online forums. It falls under the basic electronics engineering.
Try to inspect google spread sheet and copy the EXACT styles to this project