body {
    margin: 0;
    font-family: 'Segoe UI', sans-serif;
    background: #f5f7fa;
}

.topbar {
    background: #111;
    color: white;
    padding: 25px;
    text-align: center;
}

.layout {
    display: flex;
    height: calc(100vh - 120px);
}

.sidebar {
    width: 280px;
    background: white;
    border-right: 1px solid #ddd;
    overflow-y: auto;
}

.sidebar ul {
    list-style: none;
    padding: 0;
    margin: 0;
}

.sidebar li {
    padding: 15px 20px;
    cursor: pointer;
    border-bottom: 1px solid #eee;
    transition: 0.3s;
}

.sidebar li:hover {
    background: #f0f0f0;
}

.sidebar li.active {
    background: #111;
    color: white;
    font-weight: bold;
}

.content {
    flex: 1;
    padding: 40px;
    overflow-y: auto;
    background: #ffffff;
}

.unit-content {
    display: none;
    animation: fade 0.3s ease-in-out;
}

.unit-content.active {
    display: block;
}

h2 {
    margin-top: 0;
}

@keyframes fade {
    from {opacity: 0;}
    to {opacity: 1;}
}