#game {
    width: 500px;
    height: 200px;
    border: 1px solid teal;
    margin-left: auto;
    margin-right: auto;
}

.b {
    max-width: fit-content;
    margin-inline: auto;
}

#runner {
    width: 20px;
    height: 50px;
    background-color: chartreuse;
    position: relative;
    top: 150px;
}
.animate{
    animation: jump 500ms;
}
@keyframes jump {
    0%{top: 150px;}
    30%{top: 100px;}
    70%{top: 100px;}
    100%{top: 150px;}
}

#block {
    width: 20px;
    height: 20px;
    background-color: orange;
    position: relative;
    top: 130px;
    left: 480px;
    animation: block 1s infinite linear;
}
@keyframes block {
    0%{left: 480px;}
    50%{left: 210px;}
    100%{left: -40px}
}