CSS auto vertical scrollbar only

http://stackoverflow.com/a/29630320/923745

HTML

<div id="container">
    <div id="content"></div>
</div>

<label><input type="checkbox"/>Taller content</label>

CSS

#container {
    height: 300px;
    overflow-y: auto;
    overflow-x: auto;
    width: 300px;
}

#content {
    background: gray;
    background: linear-gradient(to bottom, #fffdff 0%,#00b000 100%);
    height: 300px;
}

#content.taller {
    height: 800px;
}

JavaScript

var checkbox = document.querySelector("input[type=checkbox]");
var content = document.getElementById("content");

checkbox.addEventListener("change", function(event) {
    content.className = checkbox.checked ? "taller" : "";
});