:root {
    /* Color Palette */
    --bg-color: #0f172a;
    --calc-bg: rgba(30, 41, 59, 0.7);
    --calc-border: rgba(255, 255, 255, 0.1);
    --calc-shadow: 0 25px 50px -12px rgba(0, 0, 0, 0.5);
    
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    
    --btn-bg: rgba(255, 255, 255, 0.05);
    --btn-bg-hover: rgba(255, 255, 255, 0.1);
    --btn-bg-active: rgba(255, 255, 255, 0.15);
    
    --btn-operator: rgba(14, 165, 233, 0.2);
    --btn-operator-text: #38bdf8;
    --btn-operator-hover: rgba(14, 165, 233, 0.3);
    
    --btn-action: rgba(244, 63, 94, 0.2);
    --btn-action-text: #fb7185;
    --btn-action-hover: rgba(244, 63, 94, 0.3);
    
    --btn-equals: #0ea5e9;
    --btn-equals-hover: #0284c7;
    --btn-equals-text: #ffffff;
}

* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Inter', sans-serif;
    background-color: var(--bg-color);
    background-image: 
        radial-gradient(at 0% 0%, rgba(14, 165, 233, 0.15) 0px, transparent 50%),
        radial-gradient(at 100% 100%, rgba(244, 63, 94, 0.15) 0px, transparent 50%);
    color: var(--text-primary);
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
}

.calculator-container {
    padding: 2rem;
}

.calculator {
    background: var(--calc-bg);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border: 1px solid var(--calc-border);
    border-radius: 24px;
    padding: 24px;
    width: 320px;
    box-shadow: var(--calc-shadow);
}

.display {
    text-align: right;
    margin-bottom: 24px;
    padding: 16px 8px;
    min-height: 100px;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    word-wrap: break-word;
    word-break: break-all;
}

.previous-operand {
    color: var(--text-secondary);
    font-size: 1rem;
    min-height: 1.5rem;
    margin-bottom: 4px;
    font-weight: 400;
}

.current-operand {
    color: var(--text-primary);
    font-size: 2.5rem;
    font-weight: 600;
    line-height: 1.1;
    letter-spacing: -1px;
}

.keypad {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 12px;
}

.btn {
    border: none;
    outline: none;
    background: var(--btn-bg);
    color: var(--text-primary);
    font-family: 'Inter', sans-serif;
    font-size: 1.25rem;
    font-weight: 500;
    border-radius: 16px;
    height: 60px;
    cursor: pointer;
    transition: all 0.2s ease;
    display: flex;
    justify-content: center;
    align-items: center;
}

.btn:hover {
    background: var(--btn-bg-hover);
    transform: translateY(-1px);
}

.btn:active {
    background: var(--btn-bg-active);
    transform: translateY(1px);
}

.btn-operator {
    background: var(--btn-operator);
    color: var(--btn-operator-text);
}

.btn-operator:hover {
    background: var(--btn-operator-hover);
}

.btn-action {
    background: var(--btn-action);
    color: var(--btn-action-text);
}

.btn-action:hover {
    background: var(--btn-action-hover);
}

.btn-equals {
    background: var(--btn-equals);
    color: var(--btn-equals-text);
}

.btn-equals:hover {
    background: var(--btn-equals-hover);
}

.span-2 {
    grid-column: span 2;
    border-radius: 30px; /* Pill shape for wider button */
}

/* Micro-animations on load */
@keyframes slideUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.calculator {
    animation: slideUp 0.6s cubic-bezier(0.16, 1, 0.3, 1) forwards;
}