body {
    font-family: Arial, sans-serif;
    background-color: #f4f6f7;
    margin: 0;
    padding: 0;
}

header {
    background-color: #1f7a1f;
    color: white;
    text-align: center;
    padding: 20px;
}

nav {
    text-align: center;
    margin-top: 40px;
}

nav ul {
    list-style: none;
    padding: 0;
}

nav li {
    margin: 15px 0;
}

nav a {
    text-decoration: none;
    font-size: 20px;
    color: #1f7a1f;
    font-weight: bold;
}

nav a:hover {
    text-decoration: underline;
}

header, footer {
    padding-left: 20px;
    padding-right: 20px;
}

footer {
    text-align: center;
    margin-top: 50px;
    padding: 20px;
    background-color: #ddd;
}

.intro p {
    text-align: center;
}

main {
    padding: 20px;
    max-width: 1000px;
    margin: auto;
}

.excel-frame {
    width: 100%;
    height: 800px;
    border: 3px solid red;
    background: white;
}

.container {
    max-width: 900px;
    margin: auto;
    padding: 20px;
}

p {
    font-size: 18px;
    line-height: 1.6;
    margin-bottom: 20px;
}

h2 {
    text-align: center;
    margin-top: 20px;
}

p {
    text-align: justify;
}

.main-image {
    display: block;
    margin: 30px auto;
    max-width: 100%;
    border-radius: 10px;
}

/* Layout */
.layout {
    display: flex;
    max-width: 1200px;
    margin: auto;
    align-items: flex-start;
}

/* Sidebar */
.sidebar {
    width: 200px;
    background-color: #f0f0f0;
    padding: 20px;
}

.sidebar a {
    display: block;
    margin: 10px 0;
    text-decoration: none;
    color: #1f7a1f;
    font-weight: bold;
}

.sidebar a:hover {
    text-decoration: underline;
}

/* Content */
.content {
    flex: 1;
    padding: 20px;
}

.content iframe {
    width: 100%;
    height: 800px;
    border: none;
    background: white;
}

.topnav a.active {
    background-color: #1f7a1f;
    color: white;
}