html, body {
    margin: 0;
    padding: 0;
    min-height: 100%; /* Allows document to extend as content grows */
    /* If you need to hide the scrollbar, you can add scrollbar styles here */
}

/* Starfield layers: fixed, full-viewport divs */
.star-layer {
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100vh;
    background-repeat: repeat;
    background-size: cover;
    background-attachment: scroll;
    background-position: center top;
}

/* Starfield layers (images 1–17) */
#layer1  { background-image: url('images/1.png');  z-index: 100; }
#layer2  { background-image: url('images/2.png');  z-index: 95; }
#layer3  { background-image: url('images/3.png');  z-index: 90; }
#layer4  { background-image: url('images/4.png');  z-index: 85; }
#layer5  { background-image: url('images/5.png');  z-index: 80; }
#layer6  { background-image: url('images/6.png');  z-index: 75; }
#layer7  { background-image: url('images/7.png');  z-index: 70; }
#layer8  { background-image: url('images/8.png');  z-index: 65; }
#layer9  { background-image: url('images/9.png');  z-index: 60; }
#layer10 { background-image: url('images/10.png'); z-index: 55; }
#layer11 { background-image: url('images/11.png'); z-index: 50; }
#layer12 { background-image: url('images/12.png'); z-index: 45; }
#layer13 { background-image: url('images/13.png'); z-index: 40; }
#layer14 { background-image: url('images/14.png'); z-index: 35; }
#layer15 { background-image: url('images/15.png'); z-index: 30; }
#layer16 { background-image: url('images/16.png'); z-index: 25; }
#layer17 { background-image: url('images/17.png'); z-index: 20; }

/* Layer 18: background galaxies */
#layer18 { 
    background: #000; 
    z-index: 15; 
}