body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background: #1e1e2f;
    font-family: Arial, sans-serif;
}

#calc {
    background: #2c2c3e;
    padding: 20px;
    border-radius: 15px;
    box-shadow: 0 5px 15px rgba(0,0,0,0.5);
    width: 260px;
}

#screen {
    width: 100%;
    height: 50px;
    font-size: 20px;
    text-align: right;
    padding: 10px;
    border: none;
    border-radius: 8px;
    margin-bottom: 15px;
    background: #000;
    color: #0f0;
}

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

button {
    padding: 15px;
    font-size: 18px;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    background: #3b3b5c;
    color: white;
    transition: 0.2s;
}

button:hover {
    background: #57578a;
}

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

/* Special buttons */
button:nth-child(4n) {
    background: #ff9500;
}

button:nth-last-child(2) {
    background: red;
}

button:nth-last-child(1) {
    background: green;
}