* {
    margin: 0;
    padding: 0;
}
body {
    text-align: center;
}
.container {
    width: 900px;
    margin: 20px auto 50px;
    overflow: auto;
}
.big-img{
    width: 900px;
    height: 500px;
}
.thumb {
    width: 300px;
    float: left;
}
.thumb:hover {
    opacity: 0.5;
    cursor: pointer;
}

@keyframes fadeIn {
    to {
        opacity: 1;
    }
}

.fade {
    opacity: 0;
    animation: fadeIn 0.5s forwards;
}

.active {
    opacity: 0.5;
}