* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

html, body {
    width: 100%;
    height: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: #121212;
    color: #ffffff;
}

.container {
    width: 100%;
    max-width: 400px;
    padding: 20px;
}

.calculator {
    background-color: #1e1e1e;
    border-radius: 20px;
    padding: 20px;
    box-shadow: 0 10px 30px rgba(0, 0, 0, 0.5);
}

.display {
    margin-bottom: 20px;
}

#display {
    width: 100%;
    height: 80px;
    background-color: #2d2d2d;
    border: none;
    border-radius: 10px;
    color: #ffffff;
    font-size: 2.5rem;
    text-align: right;
    padding: 10px 20px;
    outline: none;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 15px;
}

.btn {
    padding: 20px;
    font-size: 1.2rem;
    border: none;
    border-radius: 10px;
    cursor: pointer;
    background-color: #333333;
    color: #ffffff;
    transition: background-color 0.2s, transform 0.1s;
}

.btn:hover {
    background-color: #444444;
}

.btn:active {
    transform: scale(0.95);
}

/* Operator buttons */
.btn:nth-child(4),
.btn:nth-child(8),
.btn:nth-child(12),
.btn:nth-child(16),
.btn:nth-child(18),
.btn:nth-child(24),
.btn:nth-child(28) {
    background-color: #ff9f0a;
    color: #000000;
    font-weight: bold;
}

.btn:nth-child(4):hover,
.btn:nth-child(8):hover,
.btn:nth-child(16):hover,
.btn:nth-child(18):hover,
.btn:nth-child(24):hover,
.btn:nth-child(28):hover {
    background-color: #ffb03b;
}


.btn:nth-child(1),
.btn:nth-child(2) {
    background-color: #a5a5a5;
    color: #000000;
    font-weight: bold;
}

.btn:nth-child(1):hover,
.btn:nth-child(2):hover {
    background-color: #d4d4d2;
}