flappy.css

body
{
    margin: 0;
    overflow-x: hidden;
    background-color: black;
    /* background-image: url("https://i.pinimg.com/originals/e5/cc/0a/e5cc0ace6d6c25513cc25a3b8bf20516.gif"); */
    background-repeat: no-repeat;
    background-size: 100%;
}

.Block
{
    /* background-image: url("https://images.freecreatives.com/wp-content/uploads/2016/04/Solid-Color-Purple-Background-.jpg"); */
    margin-top: 0;
    top: 0;
    left: -10vw;
    right: -10vw;
    margin-left: 110vw;
    position: absolute;
    height: 20vh;
    width: 10vw;
    background-color: rgb(255, 255, 255);
    animation: Move 5s;
    animation-timing-function: linear;
}

.Ground
{
    margin-bottom: 0;
    left: -10vw;
    right: -10vw;
    bottom: 0;
    margin-left: 110vw;
    position: absolute;
    height: 20vh;
    width: 10vw;
    background-color: rgb(255, 255, 255);
    animation: Move 5s;
    animation-timing-function: linear;
}

@keyframes Move
{
    0% {margin-left: 110vw}
    100% {margin-left: -10vw}
}

.Obstacle
{
    height: 20vh;
    width: 10vw;
    background-color: black;
}

.Cube
{
    height: 16.5vh;
    width: 8vw;
    background-color: aqua;
    margin-top: 45vh;
    margin-left: 25vh;
    /* animation: KeepDown 3s;
    animation-timing-function: linear; */
}

@keyframes KeepDown
{
    0% {margin-top: 45vh;}
    100% {margin-top: 100vh;}
}