index.css

/* default styles */
* {
    padding: 0px;
    margin: 0px;
    box-sizing: border-box;
    font-family: Segoe UI, sans-serif;
    transition-duration: 0.25s;
    text-align: center;
}

/* page header */
header {
    background-color: #48d1cc;
    color: #000000;
    width: 100%;
    padding: 10px;
    margin-bottom: 15px;
}
header h1 {
    font-size: 25px;
}

/* simulation links */
#simulationLinks {
    padding: 15px;
    padding-top: 0px;
}
#simulationLinks a {
    display: inline-block;
    margin: 15px;
    line-height: 50px;
    width: 200px;
    background-color: #E0E0E0;
    color: #000000;
    text-decoration: none;
}
#simulationLinks a:hover, #simulationLinks a:focus {
    box-shadow: 0 0 15px #808080;
    transform: scale(1.1);
}
@media only screen and (max-width: 500px) {
    #simulationLinks a {
        width: calc(100% - 30px);
    }
}

/* dark mode */
@media only screen and (prefers-color-scheme: dark) {
    body {
        background: #202020;
        color: #e0e0e0;
    }
    #simulationLinks a {
        background: #404040;
        color: #e0e0e0;
    }
}