1 parameter: pad top, right, bottom, left equally
.pad1 {
   padding: 4px;
}
2 parameters: pad top and bottom with 1st value, left and right with 2nd value
.pad2 {
   padding: 4px 8px;
}
4 parameters: pad top, right, bottom, left individually
.pad4 {
   padding: 2px 4px 6px 8px;
}
Do you have TRouBLe remembering the parameter order for 4 parameters?
T - top
R - right
B - bottom
L - left