body {
    font-family: 'Arial', sans-serif;
    background-color: #f4f4f4;
    margin: 0;
    padding: 0;
    display: flex;
    flex-direction: column;
    align-items: center;
    height: 100vh;
}

header {
    text-align: center;
    margin: 20px 0;
}

nav {
    margin: 20px 0;
}

.nav-btn {
    background-color: #0078d4;
    color: white;
    border: none;
    padding: 10px 20px;
    margin: 5px;
    cursor: pointer;
    transition: background-color 0.3s;
}

.nav-btn:hover {
    background-color: #005a9e;
}

.content-section {
    display: none;
    text-align: left;
    width: 80%;
    max-width: 800px;
    margin: 20px 0;
    opacity: 0;
    transition: opacity 0.5s;
}

.content-section.active {
    display: block;
    opacity: 1;
}

h2 {
    color: #0078d4;
    border-bottom: 2px solid #0078d4;
    padding-bottom: 5px;
}

.counter {
    text-align: center;
    font-size: 1.5em;
    color: #0078d4;
    margin-top: 20px;
}