/* Basic Setup */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Poppins', sans-serif;
}

body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    /* Golden Blue Aesthetic */
    background: linear-gradient(135deg, #0f0c29, #302b63, #24243e);
    /* Deep Blue Base */
    background: radial-gradient(circle at top right, rgba(255, 215, 0, 0.15), transparent 40%),
        radial-gradient(circle at bottom left, #004e92, transparent 50%),
        linear-gradient(135deg, #0f2027, #203a43, #2c5364);
}

.container {
    padding: 20px;
}

/* Calculator Glassmorphism Container */
.calculator {
    width: 350px;
    background: rgba(20, 20, 30, 0.6);
    backdrop-filter: blur(20px);
    -webkit-backdrop-filter: blur(20px);
    border-radius: 25px;
    padding: 25px;
    box-shadow: 20px 20px 50px rgba(0, 0, 0, 0.5),
        -5px -5px 15px rgba(255, 255, 255, 0.05),
        0 0 20px rgba(255, 215, 0, 0.1);
    /* Subtle Gold Glow */
    border: 1px solid rgba(255, 215, 0, 0.2);
    /* Gold Border */
}

/* Display Screen */
.display {
    width: 100%;
    margin-bottom: 25px;
    padding: 20px;
    text-align: right;
    border-radius: 15px;
    /* Inner shadow for "screen" effect */
    background: rgba(0, 0, 0, 0.3);
    box-shadow: inset 2px 2px 10px rgba(0, 0, 0, 0.3);
    min-height: 100px;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    border-bottom: 1px solid rgba(255, 215, 0, 0.1);
}

#previous-operand {
    font-size: 1rem;
    color: rgba(255, 215, 0, 0.6);
    /* Gold Tint */
    margin-bottom: 5px;
    min-height: 1.2rem;
}

#current-operand {
    font-size: 2.5rem;
    color: #fff;
    font-weight: 500;
    word-break: break-all;
}

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

/* Button Styling - Neumorphism/Soft feel */
.btn {
    border: none;
    outline: none;
    padding: 15px;
    font-size: 1.25rem;
    font-weight: 500;
    color: #fff;
    background: linear-gradient(145deg, #2d2d2d, #1a1a1a);
    border-radius: 50%;
    cursor: pointer;
    box-shadow: 5px 5px 10px rgba(0, 0, 0, 0.5),
        -2px -2px 10px rgba(255, 255, 255, 0.05);
    transition: all 0.2s ease;
    user-select: none;
    aspect-ratio: 1;
    display: flex;
    align-items: center;
    justify-content: center;
}

.btn:hover {
    transform: translateY(-2px);
    box-shadow: 7px 7px 15px rgba(0, 0, 0, 0.6),
        -2px -2px 10px rgba(255, 255, 255, 0.1);
    border: 1px solid rgba(255, 215, 0, 0.2);
}

.btn:active {
    transform: translateY(2px);
    box-shadow: inset 3px 3px 10px rgba(0, 0, 0, 0.6),
        inset -1px -1px 5px rgba(255, 255, 255, 0.05);
}

/* Operator Keys - Pop Color */
.operator {
    color: #FFD700;
    /* Gold */
    font-weight: 600;
    text-shadow: 0 0 5px rgba(255, 215, 0, 0.3);
}

/* Function Keys (AC, DEL) - Warning/Action Color */
.function {
    color: #ff6b6b;
    font-weight: 600;
}

/* Equal Button - Prominent */
.equal {
    grid-column: span 2;
    aspect-ratio: auto;
    border-radius: 30px;
    background: linear-gradient(90deg, #FFD700, #FFA500);
    /* Gold Gradient */
    color: #1a1a1a;
    font-weight: 700;
    box-shadow: 0 0 15px rgba(255, 215, 0, 0.4);
}

.equal:hover {
    box-shadow: 0 0 25px rgba(255, 215, 0, 0.7);
    color: #1a1a1a;
}

.zero {
    /* grid-column: span 2; Removed to make 0 standard size */
    aspect-ratio: auto;
    border-radius: 50%;
    /* Make circular */
    justify-content: center;
    /* Center text */
    padding-left: 0;
    /* Remove extra padding */
}