How to avoid overlapping between two divs positioning absolute inside a div positioning relative?

absolute, css, html, overlap

Solution

Ok, I got an equivalent result by changing approach.

CSS (JSFiddle):

#div-chatroom {
    position: relative;
    height: calc(100% - 70px); /* IE9+ and future browsers */
    height: -moz-calc(100% - 70px); /* Firefox */
    height: -webkit-calc(100% - 70px); /* Chrome, Safari */
    padding: 0;
    text-align: center;
    margin: 0;
    border-right: 2px solid #333333;
    background-color: #ffffff;
    overflow: auto;
}

#div-messages {
    position: relative;
    margin: 0;
    padding: 0;    
    min-height: 200px;
    height: calc(100% - 100px); /* IE9+ and future browsers */
    height: -moz-calc(100% - 100px); /* Firefox */
    height: -webkit-calc(100% - 100px); /* Chrome, Safari */
    background-color: green;
    overflow: auto;
}

#div-sending {
    position: relative;
    margin: 0;
    padding: 0;    
    height: 100px;
    background-color: red;
}

Problem

The following code works if the page has enough space to host all divs, but if I resize at minimum the page the two divs positioning absolute overlap. How can I avoid that? ``` #div-chatroom { position: relative; height: calc(100% - 70px); /* IE9+ and future browsers */ height: -moz-calc(100% - 70px); /* Firefox */ height: -webkit-calc(100% - 70px); /* Chrome, Safari */ padding: 0; text-align: center; margin: 0; border-right: 2px solid #333333; overflow: auto; } #div-messages { position: absolute; top: 10px; bottom: 110px; left: 10px; right: 10px; min-height: 200px; overflow: auto; } #div-sending { position: absolute; bottom: 10px; left: 10px; right: 10px; height: 100px; } ``` ``` <div id="div-chatroom"> <div id="div-messages">messages here</div> <div id="div-sending">sending tools here</div> </div> ``` UPDATE #1 As required the code on JSFiddle (but if the two divs have `position: absolute` it doesn't seem to work).

Original source