body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    background: linear-gradient(45deg, #2c3e50, #3498db);
    flex-direction: column;
}

.calculator {
    background: rgba(255, 255, 255, 0.1);
    padding: 25px;
    border-radius: 20px;
    box-shadow: 0 8px 25px rgba(0, 0, 0, 0.2);
    backdrop-filter: blur(10px);
    border: 1px solid rgba(255, 255, 255, 0.1);
    max-width: 350px;
    width: 100%;
}

#display {
    width: 100%;
    height: 70px;
    font-size: 2.5rem;
    text-align: right;
    padding: 15px;
    margin-bottom: 20px;
    border: none;
    background: rgba(255, 255, 255, 0.1);
    color: white;
    border-radius: 10px;
    box-shadow: inset 0 2px 5px rgba(0, 0, 0, 0.2);
}

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

button {
    width: 100%;
    height: 65px;
    font-size: 1.5rem;
    border: none;
    cursor: pointer;
    background: rgba(255, 255, 255, 0.1);
    color: white;
    border-radius: 12px;
    transition: all 0.3s ease;
    backdrop-filter: blur(5px);
    border: 1px solid rgba(255, 255, 255, 0.1);
}

button:hover {
    background: rgba(255, 255, 255, 0.2);
    transform: translateY(-2px);
    box-shadow: 0 5px 15px rgba(0, 0, 0, 0.2);
}

button:active {
    transform: translateY(0);
}

.zero {
    grid-column: span 2;
}

button.operator {
    background: rgba(52, 152, 219, 0.3);
    font-weight: bold;
}

button.clear {
    background: rgba(231, 76, 60, 0.3);
    color: #fff;
}

button.equals {
    background: rgba(46, 204, 113, 0.3);
    grid-row: span 2;
    height: 100%;
}

.copyright {
    color: rgba(255, 255, 255, 0.7);
    font-size: 0.9rem;
    margin-top: 20px;
    text-align: center;
    font-weight: 300;
    letter-spacing: 0.5px;
    user-select: none;
}