CSS - Min height inheritance

So you know how when you use something like height 100%, it’s based on the height value that was explicitly set on a parent element?

Well, it doesn’t work when said parent element has a min-height attriubute:

#a {
    background: cyan;
    min-height: 500px;
}

#b {
    height: 100%;
    background: mistyrose;
}

I was able to get around this by giving the child element position: absolute and giving the parent position: relative.

#a {
    background: cyan;
    min-height: 500px;
    position: relative;
}

#b {
    height: 100%;
    background: mistyrose;
    position; absolute;
}