body {
    background-color: #f0f8ff;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    color: #333333;
}

h1, h2, h3 {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    color: #333333;
}

a {
    color: #006400;
    text-decoration: none;
}

a:hover {
    text-decoration: underline;
}

.button {
    background-color: #008000;
    border: none;
    color: white;
    padding: 10px 24px;
    text-align: center;
    text-decoration: none;
    display: inline-block;
    font-size: 16px;
    transition-duration: 0.4s;
    cursor: pointer;
}

.button:hover {
    background-color: #45a049;
    color: white;
}

.card {
    background-color: #ffffff;
    border-radius: 10px;
    box-shadow: 0 4px 8px 0 rgba(0,0,0,0.2);
    margin: 10px;
    padding: 16px;
    text-align: center;
    font-size: 18px;
}

.grid-container {
    display: grid;
    grid-template-columns: auto auto auto auto;
    padding: 10px;
}

.grid-item {
    background-color: rgba(255, 255, 255, 0.8);
    border: 1px solid rgba(0, 0, 0, 0.8);
    padding: 20px;
    font-size: 30px;
    text-align: center;
    cursor: pointer;
    user-select: none;
}

.hidden {
    visibility: hidden;
}