The position property specifies the type of positioning method used for an element (static, relative, absolute, fixed, or sticky).
In the below-given example, no height is specified in percentage and no jQuery is needed
.mainbody{
position: absolute;//here we are setting the position of an element as absolute
top: 30px; /* here we are defining Header Height to 30 px */
bottom: 10px; /*here we are defining Footer Height to 10 px */
width: 100%;// here we are setting the width to 100%
}