body {
    margin: 0;
    font-family: Arial, sans-serif;
    background-color: #121212;
    color: #ffffff;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    height: 100vh;
}
.container {
    width: 100%;
    height: 100%;
    display: grid;
    grid-template-columns: repeat(2, 1fr);
    grid-template-rows: repeat(2, 1fr);
}
.bg-section {
    background-size: cover;
    background-position: center;
    position: relative;
    transition: transform 0.6s ease;
}
.popup-message {
    display: none;
    color: #ffffff;
    font-size: 1em;
    margin-top: 10px;
    transition: opacity 1s ease;
    opacity: 0;
}
.bg-section:nth-child(1) {
    background-image: url('../images/beijing.jpg');
}
.bg-section:nth-child(2) {
    background-image: url('../images/shanghai.jpg');
}
.bg-section:nth-child(3) {
    background-image: url('../images/guangzhou.jpg');
}
.bg-section:nth-child(4) {
    background-image: url('../images/shenzhen.jpg');
}
.bg-section:active {
    transform: scale(1.05);
}
.overlay {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    background-color: rgba(0, 0, 0, 0.7);
    padding: 20px;
    border-radius: 10px;
    text-align: center;
    max-width: 600px;
    width: 90%;
}
h1 {
    font-size: 2.5em;
    margin-bottom: 20px;
}
p {
    font-size: 1.2em;
    margin-bottom: 20px;
}
.cta-button {
    display: block;
    background-color: #ff5722;
    color: #ffffff;
    padding: 15px 30px;
    font-size: 1.2em;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    text-decoration: none;
    margin-top: 20px;
}
.cta-button:hover {
    background-color: #e64a19;
}
.popup-message {
    display: none;
    color: #ffffff;
    font-size: 1em;
    margin-top: 10px;
}
@media (max-width: 600px) {
    h1 {
        font-size: 2em;
    }
    p {
        font-size: 1em;
    }
    .cta-button {
        font-size: 1em;
        padding: 10px 20px;
    }
    .popup-message {
        font-size: 0.9em;
    }
}