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

body {
    background: linear-gradient(135deg, #202020, #3a3a3a);
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    height: 100vh;
}

.calculator {
    background: rgba(255, 255, 255, 0.05);
    border-radius: 25px;
    padding: 20px;
    box-shadow: 0 8px 32px 0 rgba(31, 38, 135, 0.37);
    backdrop-filter: blur(10px);
    display: grid;
    width: 90%;
    max-width: 340px;
}

.display {
    background: rgba(255, 255, 255, 0.1);
    color: #fff;
    font-size: 2.5rem;
    text-align: right;
    padding: 20px;
    border-radius: 15px;
    margin-bottom: 20px;
    min-height: 60px;
    user-select: none;
}

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

button {
    font-size: 1.4rem;
    padding: 20px;
    border: none;
    border-radius: 15px;
    background: rgba(255, 255, 255, 0.1);
    color: white;
    cursor: pointer;
    transition: all 0.2s ease;
    backdrop-filter: blur(5px);
    min-height: 60px;
    user-select: none;
}

button:hover {
    background: rgba(255, 255, 255, 0.2);
    transform: scale(1.05);
}

button:active {
    transform: scale(0.98);
    opacity: 0.8;
}

button:nth-child(-n+4) {
    background: rgba(255, 255, 255, 0.15);
}

.equal {
    grid-column: span 2;
    background: linear-gradient(to right, #00c6ff, #0072ff);
    color: white;
    font-weight: bold;
}

.equal:hover {
    background: linear-gradient(to right, #0072ff, #00c6ff);
}

.footer {
    margin-top: 10px;
    text-align: center;
    font-size: 1rem;
    color: #ccc;
    font-weight: 300;
    backdrop-filter: blur(5px);
    padding: 10px 0;
    width: 100%;
}

.footer span {
    color: #00c6ff;
    font-weight: 500;
    cursor: pointer;
}