body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    background-color: #1a1a1a;
    font-family: 'Roboto', sans-serif;
    margin: 0;
}

.calculator {
    background: linear-gradient(145deg, #1f1f1f, #242424);
    border-radius: 20px;
    box-shadow: 8px 8px 16px #141414, -8px -8px 16px #2e2e2e;
    padding: 20px;
    width: 320px;
}

.display {
    margin-bottom: 20px;
}

.display input {
    width: 100%;
    height: 60px;
    background-color: #1a1a1a;
    border: none;
    border-radius: 10px;
    box-shadow: inset 4px 4px 8px #141414, inset -4px -4px 8px #2e2e2e;
    color: #00ffab;
    font-size: 2rem;
    padding: 10px;
    text-align: right;
    outline: none;
}

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

.btn {
    background-color: #1a1a1a;
    border: none;
    border-radius: 10px;
    box-shadow: 4px 4px 8px #141414, -4px -4px 8px #2e2e2e;
    color: #00ffab;
    font-size: 1.5rem;
    padding: 20px;
    cursor: pointer;
    transition: all 0.2s ease;
    position: relative;
    overflow: hidden;
}

.btn:hover {
    background-color: #00ffab;
    color: #1a1a1a;
}

.btn:before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 300%;
    height: 300%;
    background: rgba(255, 255, 255, 0.15);
    transition: all 0.75s ease;
    transform: translate(-50%, -50%) rotate(45deg);
    opacity: 0;
}

.btn:hover:before {
    width: 0;
    height: 0;
    opacity: 1;
}

.zero {
    grid-column: span 2;
}