.videowrapper {
    float: none;
    clear: both;
    width: 100%;
    position: relative;
    padding-bottom: 56.25%;
    padding-top: 25px;
    height: 0;
}

    .videowrapper iframe {
        position: absolute;
        top: 0;
        left: 0;
        width: 100%;
        height: 100%;
    }