/* =============================================================================
   Stardust Calculator Styling Sheets (Vanilla CSS)
   ============================================================================= */

:root {
    --bg-dark: #050510;
    --font-heading: 'Space Grotesk', sans-serif;
    --font-body: 'Outfit', sans-serif;
    
    /* Neon Glow Color Palette */
    --color-digit: rgba(255, 255, 255, 0.9);
    --color-digit-hover: rgba(255, 255, 255, 1);
    
    --color-operator: #00E5FF;
    --color-operator-hover: #e0f7fa;
    --border-operator: rgba(0, 229, 255, 0.35);
    --glow-operator: 0 0 15px rgba(0, 229, 255, 0.4);
    
    --color-danger: #FF5252;
    --border-danger: rgba(255, 82, 82, 0.35);
    --glow-danger: 0 0 15px rgba(255, 82, 82, 0.4);
    
    --color-warning: #FF8A65;
    --border-warning: rgba(255, 138, 101, 0.35);
    --glow-warning: 0 0 15px rgba(255, 138, 101, 0.4);
    
    --color-equals: #FFD740;
    --border-equals: rgba(255, 215, 64, 0.4);
    --glow-equals: 0 0 20px rgba(255, 215, 64, 0.65);
    
    --glass-border: rgba(94, 53, 177, 0.25);
    --glass-border-hover: rgba(179, 136, 255, 0.5);
    --glass-shadow: 0 16px 40px rgba(0, 0, 0, 0.6), inset 0 1px 1px rgba(255, 255, 255, 0.1);
}

/* Reset and Layout Foundation */
* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

body {
    background-color: var(--bg-dark);
    font-family: var(--font-body);
    min-height: 100vh;
    overflow: hidden;
    position: relative;
    display: flex;
    justify-content: center;
    align-items: center;
    color: #ffffff;
}

/* Stellar Backdrop Canvas */
#space-canvas {
    position: absolute;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    z-index: 0;
    pointer-events: none; /* Allows click events to pass down to buttons */
}

/* Main Container Layout */
.calculator-container {
    position: relative;
    z-index: 10;
    width: 100%;
    max-width: 400px;
    padding: 20px;
}

/* Premium Glassmorphic Calculator Outer Shell */
.calculator-shell {
    background: rgba(13, 9, 31, 0.45);
    backdrop-filter: blur(16px);
    -webkit-backdrop-filter: blur(16px);
    border: 1.5px solid var(--glass-border);
    border-radius: 24px;
    padding: 24px;
    box-shadow: var(--glass-shadow);
    transition: border-color 0.4s ease, box-shadow 0.4s ease;
}

.calculator-shell:hover {
    border-color: rgba(94, 53, 177, 0.35);
    box-shadow: 0 20px 48px rgba(0, 0, 0, 0.7), 0 0 30px rgba(126, 87, 194, 0.15);
}

/* Visually Hidden for SEO/Accessibility */
.visually-hidden {
    position: absolute;
    width: 1px;
    height: 1px;
    padding: 0;
    margin: -1px;
    overflow: hidden;
    clip: rect(0, 0, 0, 0);
    white-space: nowrap;
    border: 0;
}

/* Calculator Screen Display */
.display-container {
    background: rgba(8, 5, 20, 0.6);
    border: 1.5px solid rgba(126, 87, 194, 0.3);
    border-radius: 16px;
    padding: 20px;
    min-height: 120px;
    margin-bottom: 24px;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    align-items: flex-end;
    overflow: hidden;
    text-align: right;
    box-shadow: inset 0 2px 8px rgba(0, 0, 0, 0.8);
    transition: border-color 0.3s ease;
}

.calculator-shell:hover .display-container {
    border-color: rgba(126, 87, 194, 0.5);
}

.display-expr {
    font-family: var(--font-heading);
    font-size: 1.15rem;
    color: rgba(179, 136, 255, 0.85);
    min-height: 1.5rem;
    margin-bottom: 6px;
    letter-spacing: 1px;
    overflow-x: auto;
    width: 100%;
    white-space: nowrap;
    scrollbar-width: none;
}

.display-expr::-webkit-scrollbar {
    display: none;
}

.display-result {
    font-family: var(--font-heading);
    font-size: 2.85rem;
    font-weight: 700;
    color: #ffffff;
    width: 100%;
    overflow-x: auto;
    white-space: nowrap;
    scrollbar-width: none;
    transition: font-size 0.15s ease;
}

.display-result::-webkit-scrollbar {
    display: none;
}

/* Grid Layout of Keys */
.keyboard-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 14px;
}

/* Base Style for All Calculator Keys */
.btn {
    background: rgba(30, 20, 50, 0.15);
    border: 1.5px solid rgba(69, 39, 160, 0.6);
    border-radius: 16px;
    padding: 18px 0;
    font-family: var(--font-body);
    font-size: 1.45rem;
    font-weight: 600;
    color: var(--color-digit);
    cursor: pointer;
    outline: none;
    user-select: none;
    display: flex;
    justify-content: center;
    align-items: center;
    transition: all 0.25s cubic-bezier(0.25, 0.8, 0.25, 1);
    position: relative;
    overflow: hidden;
}

/* Subtle Interactive Press Effect */
.btn:active {
    transform: scale(0.92);
}

/* Hover Accent Glowing effects based on Button Role */
.btn-digit:hover {
    background: rgba(255, 255, 255, 0.08);
    border-color: var(--glass-border-hover);
    color: var(--color-digit-hover);
    box-shadow: 0 0 12px rgba(179, 136, 255, 0.25);
}

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

.btn-operator:hover {
    background: rgba(0, 229, 255, 0.08);
    border-color: var(--color-operator);
    color: #ffffff;
    box-shadow: var(--glow-operator);
}

.btn-danger {
    color: var(--color-danger);
    border-color: var(--border-danger);
}

.btn-danger:hover {
    background: rgba(255, 82, 82, 0.08);
    border-color: var(--color-danger);
    color: #ffffff;
    box-shadow: var(--glow-danger);
}

.btn-warning {
    color: var(--color-warning);
    border-color: var(--border-warning);
}

.btn-warning:hover {
    background: rgba(255, 138, 101, 0.08);
    border-color: var(--color-warning);
    color: #ffffff;
    box-shadow: var(--glow-warning);
}

.btn-equals {
    color: var(--color-equals);
    border-color: var(--border-equals);
    background: rgba(255, 215, 64, 0.08);
}

.btn-equals:hover {
    background: rgba(255, 215, 64, 0.15);
    border-color: var(--color-equals);
    color: #ffffff;
    box-shadow: var(--glow-equals);
}

/* Double Width Layout Key (Zero button) */
.btn-double {
    grid-column: span 2;
}

/* Responsive Touchups for Small Displays */
@media (max-height: 600px) {
    .calculator-container {
        padding: 10px;
    }
    .calculator-shell {
        padding: 16px;
    }
    .display-container {
        padding: 12px;
        min-height: 90px;
        margin-bottom: 16px;
    }
    .display-result {
        font-size: 2.2rem;
    }
    .btn {
        padding: 12px 0;
        font-size: 1.25rem;
        border-radius: 12px;
    }
    .keyboard-grid {
        gap: 10px;
    }
}