body {
    text-align: center;
}

.header {
    padding: 50px;
    text-align: center;
    border: 3px solid maroon;
    background: midnightblue;
    color: white;
    font-size: 30px;
}

.contentBackground {
    position: absolute;
    top: 50%;
    left: 0;
    width: 100%;
    height: 100vh;
    background: linear-gradient(to bottom, white, steelblue);
    z-index: -1;
}

#simulationBox {
    width: 800px;
    height: 500px;
    position: relative;
    background: white;
    display: block;
    margin-left: auto;
    margin-right: auto;
}

.molecules {
    position: absolute;
    top: 260px;
    left: 350px;
}
.img1 {
    position: absolute;
    top: 100px;
    left: 400px;
}

.img2 {
    position: absolute;
    top: 110px;
    left: 100px;
}

.img3 {
    position: absolute;
    top: 350px;
    left: 100px;
    z-index: 3;
}