JSFiddle - React, Tailwind, and code Playground

HTML

<div class="container">
    <iframe src="http://www.youtube.com/embed/QKh1Rv0PlOQ?rel=0&fs=1&showinfo=0&autohide=1&wmode=transparent" frameborder="0" allowfullscreen>
    </iframe>
    <div class="corner topleft"></div>
    <div class="corner topright"></div>
    <div class="corner bottomright"></div>
    <div class="corner bottomleft"></div>
</div>

CSS

.container {
    position: relative;
    max-width: 480px;
    height:360px;
}

.corner {
    background: url("http://i1272.photobucket.com/albums/y384/5kywalkar/curvedcorner30px_zps1e882af9.png") no-repeat top left;
    position: absolute;
    height: 48px;
    width: 30px;
    z-index: 99;
}
.topleft {
    left: 0;
    top: 0;
    margin-left: -9px;
    margin-top: -18px;
    -moz-transform: rotate(45deg);
    -ms-transform: rotate(45deg);
    -o-transform: rotate(45deg);
    -webkit-transform: rotate(45deg);
}
.topright {
    right: 0;
    top: 0;
    margin-right: -9px;
    margin-top: -18px;
    -moz-transform: rotate(135deg);
    -ms-transform: rotate(135deg);
    -o-transform: rotate(135deg);
    -webkit-transform: rotate(135deg);
}
.bottomright {
    bottom: 0;
    right: 0;
    margin-right: -9px;
    margin-bottom: -18px;
    -moz-transform: rotate(225deg);
    -ms-transform: rotate(225deg);
    -o-transform: rotate(225deg);
    -webkit-transform: rotate(225deg);
}
.bottomleft {
    bottom: 0;
    left: 0;
    margin-left: -9px;
    margin-bottom: -18px;
    -moz-transform: rotate(315deg);
    -ms-transform: rotate(315deg);
    -o-transform: rotate(315deg);
    -webkit-transform: rotate(315deg);
}

iframe {
    width: 100%;
    height: 100%;
}