How to make child divs always fit inside parent div?

Question

My question is if there is a way, without using JavaScript, to cause child divs to extend to the borders of their parent, without exceeding those borders, when you cannot kn

Answer 1

you could use inherit

#one {width:500px;height:300px;}
#two {width:inherit;height:inherit;}
#three {width:inherit;height:inherit;}