Given the following HTML:
Just set element child to position: relative and than move it top: 100% (that's the 100% height of the parent) and stick to bottom of parent by transform: translateY(-100%) (that's -100% of the height of the child).
BenefitS
But still just workaround :(
.copyright{
position: relative;
top: 100%;
transform: translateY(-100%);
}
Don't forget prefixes for the older browser.