SkewY with different values top and bottom

Question

I would like to make a shape where the top is skewY -10deg and the bottom is 10deg to produce the shape as seen in the picture:

I can't seem to figure out how to accomplish this.

Answer 1

Working Demo

This should do the trick:

CSS

#test {
    width: 200px;
    height: 200px;
    -webkit-transition: all 300ms ease-in;
     background: black;
    position: relative;
}

#test:after, #test:before {
    display: block;
    content: "";
    color: transparent;
    width: 215px;
    height: 50px;
    background: white;
    position: absolute;
    left: -10px;
    bottom: -20px;
    -webkit-transform: rotate(12deg);
    -moz-transform: rotate(12deg);
}
#test:before {
    bottom: auto;
    top: -20px;
    -webkit-transform: rotate(-12deg);
    -moz-transform: rotate(-12deg);
}

HTML

<div id="test"></div>