ul {
    display: flex;
    position: absolute;
    top: 50%;
    left: 50%;
    width: 90vw;
    height: 80vh;
    transform: translate(-50%, -50%);
    -webkit-transform: translate(-50%, -50%);
    -moz-transform: translate(-50%, -50%);
    -ms-transform: translate(-50%, -50%);
    -o-transform: translate(-50%, -50%);
}

ul li {
    list-style: none;
    width: 25%;
    background: url(../img/AyrtonSenna.jpg) center center;
    background-size: 100% 100% cover;
    height: 100%;
    transition: 0.5s;
    -webkit-transition: 0.5s;
    -moz-transition: 0.5s;
    -ms-transition: 0.5s;
    -o-transition: 0.5s;
}

ul:hover li:nth-child(odd) {
    transform: skewY(15deg);
    -webkit-transform: skewY(15deg);
    -moz-transform: skewY(15deg);
    -ms-transform: skewY(15deg);
    -o-transform: skewY(15deg);
    box-shadow: inset 1.5625vw 0 5.434782608695652vw rgba(0, 0, 0, .5);
}

ul:hover li:nth-child(even) {
    transform: skewY(-15deg);
    -webkit-transform: skewY(-15deg);
    -moz-transform: skewY(-15deg);
    -ms-transform: skewY(-15deg);
    -o-transform: skewY(-15deg);
    box-shadow: inset 1.5625vw 0 5.434782608695652vw rgba(0, 0, 0, .5);
}

ul li:nth-child(1) {
    background-position: 0;
}

ul li:nth-child(2) {
    background-position: -22.5vw;
}

ul li:nth-child(3) {
    background-position: calc(-22.5vw * 2);
}

ul li:nth-child(4) {
    background-position: calc(-22.5vw * 3);
}