/* Full-Screen Setup */
body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 1rem;
    margin: 0;
    font-family: 'Poppins', sans-serif;
    background: linear-gradient(135deg, #1f1c2c, #928dab);
    overflow: hidden;
}

/* Calculator Container with Glassmorphism Effect and Infinite Shadow Animation */
.calculator {
    display: flex;
    flex-direction: column;
    background: rgba(255, 255, 255, 0.1);
    padding: 20px;
    border-radius: 20px;
    backdrop-filter: blur(10px);
    border: 1px solid rgba(255, 255, 255, 0.18);
    max-width: 400px;
    width: 100%;
    margin: 0 15px;
    animation: shadowColorChange 5s infinite ease-in-out;
    box-shadow: 0 0 20px rgba(255, 0, 0, 0.5); /* Initial shadow */
}

/* Infinite Color-Changing Shadow Animation */
@keyframes shadowColorChange {
    0% {
        box-shadow: 0 0 20px rgba(255, 0, 0, 0.5);
    }
    25% {
        box-shadow: 0 0 20px rgba(0, 255, 0, 0.5);
    }
    50% {
        box-shadow: 0 0 20px rgba(0, 0, 255, 0.5);
    }
    75% {
        box-shadow: 0 0 20px rgba(255, 255, 0, 0.5);
    }
    100% {
        box-shadow: 0 0 20px rgba(255, 0, 255, 0.5);
    }
}

/* Display Screen Styling */
#display {
    font-size: 2rem;
    font-weight: 900;
    padding: 20px;
    border-radius: 15px;
    border: none;
    text-align: right;
    background: rgba(0, 0, 0, 0.15);
    color: #000000;
    margin-bottom: 30px;
    box-shadow: inset 0 4px 8px rgba(0, 0, 0, 0.25);
    transition: box-shadow 0.3s ease;
    word-wrap: break-word;
    max-width: 100%;
}

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

/* Common Button Styling */
.btn {
    background: rgba(255, 255, 255, 0.1);
    color: #000000;
    font-size: 1.5rem;
    font-weight: 800;
    padding: 20px;
    border: none;
    border-radius: 12px;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: 0 6px 12px rgba(0, 0, 0, 0.2);
    backdrop-filter: blur(4px);
}

/* Hover effect for the display */
#display:hover {
    box-shadow: inset 0 6px 12px rgba(0, 0, 0, 0.35);
}

/* Button hover effect */
.btn:hover {
    transform: translateY(-3px);
    box-shadow: 0 12px 24px rgba(255, 255, 255, 0.2);
    background: rgba(255, 255, 255, 0.3);
}

/* Button pressed effect */
.btn:active {
    transform: translateY(2px);
    background: rgba(255, 255, 255, 0.2);
}

/* Special Button Styling for Operators */
.btn.operator {
    background: linear-gradient(135deg, #ff5722, #e64a19);
    box-shadow: 0 8px 16px rgba(255, 87, 34, 0.4);
}

.btn.operator:hover {
    background: linear-gradient(135deg, #ff7043, #e64a19);
}

/* Special Button Styling for Equal */
.btn.equal {
    background: linear-gradient(135deg, #00e6b8, #00cc88);
    color: #fff;
    box-shadow: 0 8px 16px rgba(0, 230, 184, 0.4);
}

.btn.equal:hover {
    background: linear-gradient(135deg, #00ffcc, #00d8a0);
}

/* Special Button Styling for Clear */
.btn.clear {
    background: linear-gradient(135deg, #f44336, #e53935);
    color: #fff;
    box-shadow: 0 8px 16px rgba(244, 67, 54, 0.4);
}

.btn.clear:hover {
    background: linear-gradient(135deg, #ff7961, #f44336);
}

/* Large Button for Zero */
.btn.zero {
    grid-column: span 2;
}

/* Smooth Animations for Display Change */
#display {
    animation: fadeIn 0.5s ease-in-out;
}

/* Fade-in Animation for Buttons */
@keyframes fadeIn {
    from {
        opacity: 0;
        transform: translateY(-10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* Responsive Design Adjustments */

/* Small Screens (Mobile Phones) */
@media screen and (max-width: 480px) {
    #display {
        font-size: 1.8rem;
        padding: 15px;
    }

    .btn {
        font-size: 1.2rem;
        padding: 15px;
    }

    .calculator {
        max-width: 90vw;
        padding: 15px;
    }
}

/* Medium Screens (Tablets) */
@media screen and (max-width: 768px) {
    #display {
        font-size: 2rem;
        padding: 18px;
    }

    .btn {
        font-size: 1.3rem;
        padding: 18px;
    }
    
    .calculator {
        max-width: 80vw;
        padding: 18px;
    }
}