styles.css

* {
    box-sizing: border-box;
    padding: 0;
    margin: 0;
    font-family: 'Cabin Sketch', 'Fira Sans', 'Helvetica', 'Arial', sans-serif;
    text-align: center;
    color: white;
}

:root {
    --cell-size: 10rem;
    --header-height: 8rem;
}

#main {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 2rem;
    padding: 3rem;
    height: calc(100vh - 8rem);
    font-family: 'Cabin Sketch', 'Fira Sans', 'Helvetica', 'Arial', sans-serif;
}

#start-menu, #summary-menu {
    margin: auto;
    padding: 2rem;
    border-radius: 10px;
    background-color: #014232;
    font-size: 20px;
}

#start-form li {
    list-style: none;
}

#start-form input {
    color: black;
    text-align: left;
}

#header {
    background: #014232;
    height: var(--header-height);
    font-size: 5rem;
    padding-top: 1rem;
}

#main {
    background: #256F5C;
}

#board {
    display: grid;
    grid-template-columns: repeat(3, var(--cell-size));
    margin: 0 auto;
}

.cell {
    border: 3px solid white;
    width: var(--cell-size);
    height: var(--cell-size);
    font-size: var(--cell-size);
    display: flex;
    align-items: center;
    justify-content: center;
}

button {
    padding: 0.3rem;
    background-color: blue;
    color: white;
    margin-top: 1rem;
    font-size: 20px;
}