One play to tinker with
Either switch-off the gridlines
(Tools > Options > View tab > Uncheck gridlines > OK)
or press CTRL + A (select entire sheet)
then click to Fill color > white
Select the cell(s)
Click Format > Cells > Border tab
Select the thickest solid line in "Style"
Click to format either the right & bottom
or the left & top borders
Select the thinnest solid line in "Style"
Click to format the remaining 2 borders
Click OK