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

body {
    height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: #e0e5ec;
}

.calculator {
    width: 320px;
    padding: 25px;
    border-radius: 30px;
    background: #e0e5ec;
    box-shadow: 20px 20px 60px #bec3c9, -20px -20px 60px #ffffff;
}

.display {
    padding: 20px;
    margin-bottom: 25px;
    text-align: right;
    border-radius: 15px;
    background: #e0e5ec;
    box-shadow: inset 5px 5px 10px #bec3c9, inset -5px -5px 10px #ffffff;
}

.previous-operand {
    min-height: 20px;
    font-size: 14px;
    color: rgba(70, 70, 70, 0.7);
    margin-bottom: 5px;
}

.current-operand {
    font-size: 32px;
    font-weight: 500;
    color: #333;
}

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

.btn {
    height: 60px;
    border: none;
    font-size: 18px;
    font-weight: 500;
    border-radius: 15px;
    cursor: pointer;
    transition: all 0.2s ease;
    background: #e0e5ec;
    box-shadow: 5px 5px 10px #bec3c9, -5px -5px 10px #ffffff;
}

.btn:active {
    box-shadow: inset 3px 3px 5px #bec3c9, inset -3px -3px 5px #ffffff;
}

.number {
    color: #333;
}

.operator {
    color: #5c7cfa;
}

.special {
    background: linear-gradient(145deg, #5c7cfa, #4263eb);
    color: white;
    box-shadow: 5px 5px 10px #bec3c9, -5px -5px 10px #ffffff;
}

.special:active {
    box-shadow: inset 3px 3px 5px #3b53c0, inset -3px -3px 5px #4f6dde;
}

.zero {
    grid-column: span 2;
}

.equals {
    grid-row: span 1;
}

/* Hover effects */
.btn:hover {
    transform: translateY(-2px);
}

.btn:active {
    transform: translateY(0);
}

@media (max-width: 380px) {
    .calculator {
        width: 90vw;
        padding: 15px;
    }
    
    .btn {
        height: 50px;
        font-size: 16px;
    }
}