index.css

body {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    margin: 0;
    font-family: "Encode Sans",-apple-system,BlinkMacSystemFont,"Segoe UI","Roboto","Oxygen","Ubuntu","Cantarell","Fira Sans","Droid Sans","Helvetica Neue",sans-serif;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

h1 {
    text-decoration: underline;
}

.grid {
    width: 30px;
    height: 30px;
    background: rgb(238, 238, 238);
    border: 1.5px solid rgb(33, 33, 33);
    box-sizing: border-box;
    transition: background 200ms ease-in-out 0s;
}

.button {
    box-sizing: border-box;
    border-radius: 3px;
    background: white;
    border: 2px solid rgb(33, 33, 33);
    color: rgb(33, 33, 33);
    font-weight: bold;
    padding: 5px 10px;
    margin-right: 10px;
    cursor: pointer;
    margin-bottom: 10px;
}

.button:hover {
    background-color: black;
    color: white;
}

/* The slider itself */
.slider {
    -webkit-appearance: none;  /* Override default CSS styles */
    appearance: none;
    width: auto; /* Full-width */
    height: 15px; /* Specified height */
    background: #d3d3d3; /* Grey background */
    outline: none; /* Remove outline */
    opacity: 0.7; /* Set transparency (for mouse-over effects on hover) */
    direction: rtl; /* reverse direction of value */
    -webkit-transition: .2s; /* 0.2 seconds transition on hover */
    transition: opacity .2s;
}
  
/* Mouse-over effects */
.slider:hover {
    opacity: 1; /* Fully shown on mouse-over */
}
  
/* The slider handle (use -webkit- (Chrome, Opera, Safari, Edge) and -moz- (Firefox) to override default look) */
.slider::-webkit-slider-thumb {
    -webkit-appearance: none; /* Override default look */
    appearance: none;
    width: 15px; /* Set a specific slider handle width */
    height: 15px; /* Slider handle height */
    background: #04AA6D; /* Green background */
    cursor: pointer; /* Cursor on hover */
}

.slider::-moz-range-thumb {
    width: 15px; /* Set a specific slider handle width */
    height: 15px; /* Slider handle height */
    background: #04AA6D; /* Green background */
    cursor: pointer; /* Cursor on hover */
}

label[for='speed'] {
    font-weight: bold;
    font-size: 20px;
    font-family: "Encode Sans",-apple-system,BlinkMacSystemFont,"Segoe UI","Roboto","Oxygen","Ubuntu","Cantarell","Fira Sans","Droid Sans","Helvetica Neue",sans-serif;
    margin-right: 10px;
}