body {
    font-family: 'Arial', sans-serif;
    background-color: #f0f0f0;
    margin: 0;
    padding: 0;
}

header {
    background-color: #9966ff;
    padding: 10px 0;
    position: sticky;
    top: 0;
    z-index: 1000;
    box-shadow: 0 2px 5px rgba(0,0,0,0.1);
}

nav ul {
    list-style-type: none;
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: flex-start;
}

nav li {
    margin-right: 20px;
}

nav li a {
    display: block;
    color: white;
    text-align: center;
    padding: 10px 15px;
    text-decoration: none;
    transition: background-color 0.3s, color 0.3s;
    border-radius: 5px;
}

nav li a:hover, nav li a.active {
    background-color: #7a52cc;
    color: #ffffff;
}

/* Rest of your CSS remains the same */

.calculator-wrapper {
    display: flex;
    justify-content: center;
    align-items: center;
    height: calc(100vh - 70px);
    padding-top: 20px;
}

.calculator {
    width: 300px;
    background-color: #333;
    border-radius: 20px;
    padding: 20px;
    box-shadow: 0 10px 20px rgba(0,0,0,0.19), 0 6px 6px rgba(0,0,0,0.23);
}

h2 {
    color: #fff;
    text-align: center;
    margin-bottom: 20px;
    font-size: 24px;
}

#display {
    width: 100%;
    height: 60px;
    margin-bottom: 20px;
    padding: 10px;
    font-size: 24px;
    text-align: right;
    background-color: #4CAF50;
    color: white;
    border: none;
    border-radius: 10px;
    box-shadow: inset 0 2px 5px rgba(0,0,0,0.1);
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}

button {
    padding: 15px;
    font-size: 20px;
    border: none;
    border-radius: 50%;
    cursor: pointer;
    transition: all 0.3s ease;
}

button:hover {
    transform: scale(1.1);
}

button:active {
    transform: scale(0.95);
}

button:nth-child(4n), button:last-child {
    background-color: #FF9800;
    color: white;
}

button:nth-child(4n-1):not(:nth-child(3)):not(:nth-child(7)):not(:nth-child(11)):not(:nth-child(15)) {
    background-color: #2196F3;
    color: white;
}

button:nth-child(3), button:nth-child(7), button:nth-child(11), button:nth-child(15) {
    background-color: #f44336;
    color: white;
}

button:nth-child(16) {
    background-color: #4CAF50;
    color: white;
}