body {
    font-family: 'Poppins', sans-serif;
    margin: 0;
    background-color: #f4f8fb;
    color: #333;
    transition: background 0.3s, color 0.3s;
}

.navbar {
    display: flex;
    justify-content: space-between;
    align-items: center;
    background: linear-gradient(90deg, #007991, #78ffd6);
    padding: 1rem 2rem;
    color: white;
}

.logo {
    font-size: 1.5rem;
    font-weight: 600;
}

.nav-links {
    list-style: none;
    display: flex;
    gap: 1rem;
}

.nav-links li a {
    color: white;
    text-decoration: none;
    font-weight: 500;
    transition: color 0.3s;
}

.nav-links li a:hover {
    color: #002f34;
}

#theme-toggle {
    background: transparent;
    border: none;
    font-size: 1.2rem;
    cursor: pointer;
    color: white;
}

.card {
    background: white;
    max-width: 500px;
    margin: 2rem auto;
    padding: 2rem;
    border-radius: 10px;
    box-shadow: 0 4px 10px rgba(0, 0, 0, 0.1);
}

.card h2 {
    margin-bottom: 1rem;
    color: #007991;
}

input, select {
    width: 100%;
    padding: 0.6rem;
    margin-bottom: 1rem;
    border: 1px solid #ccc;
    border-radius: 5px;
}

.calc-btn {
    background: #007991;
    color: white;
    padding: 0.7rem 1rem;
    border: none;
    border-radius: 5px;
    cursor: pointer;
    font-weight: 600;
}

.calc-btn:hover {
    background: #005f6b;
}

.dark-mode {
    background-color: #1e1e1e;
    color: white;
}

.dark-mode .card {
    background-color: #2c2c2c;
}

.dark-mode .navbar {
    background: linear-gradient(90deg, #0f2027, #2c5364);
}