* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: sans-serif;
}

html, body {
    width: 100%;
    height: 100%;
    background: #0a0a0a;
    color: white;
    display: flex;
    align-items: center;
    justify-content: center;
}

#start-screen {
    text-align: center;
}

h1 {
    margin-bottom: 40px;
    font-size: 28px;
}

.mode-btn {
    display: block;
    width: 280px;
    padding: 20px;
    margin: 16px auto;
    font-size: 18px;
    border: none;
    border-radius: 12px;
    background: #222;
    color: white;
    cursor: pointer;
}

.mode-btn:active {
    background: #333;
}