style.css

body {
    margin: 0;
}

.game-container {
    display: flex;
    background-color: #444;
    width: 400px;
    height: 600px;
    align-items: center;
    justify-content: space-around;
    flex-direction: column;
    position: relative;
    overflow: hidden;
}

.line {
    background-color: #999;
    height: 100px;
    width: 10px;
    position: absolute;
    left: calc(50% - 5px);
}

#score {
    position: absolute;
    left: 10px;
    top: 5px;
    color: white;
    font-size: 3em;
}

.car {
    width: 30px;
    height: 65px;
    background-image: url('img/car.png');
    background-size: contain;
    transition-duration: 100ms;
    position: absolute;
}

.my-car {
    width: 30px;
    height: 65px;
    background-image: url('img/my-car.png');
    background-size: contain;
    background-repeat: no-repeat;
    transition-duration: 100ms;
    position: absolute;
}

#menu {
    position: absolute;
    background-color: azure;
    text-align: center;
    /* padding: 10px 0px; */
    width: 300px;
    height: 100px;
    left: 50px;
    top: 190px;
    font-family: 'Courier New', Courier, monospace;
    font-weight: 800;
    border-radius: 2px;
    box-shadow: 0px 0px 10px #444;
}

#start-btn {
    background-color: cadetblue;
    padding: 28px;
    cursor: pointer;
}

#start-btn:hover {
    background-color: #3a7072;
    color: white;
}

.header {
    padding: 18px 0px 0px 0px;
}