how to find last child in css code example

Example 1: not last child css

p:not(:last-child) { 
	margin-bottom: 20px
}

Example 2: css last child with class

/*This will only work if the last child of someEID has 
the class .myclassName 
if the last child does not have class name us js*/
#someEID .myClassName:last-child {
    background: blue;
}