/* ============================================
   SCIENTIFIC CALCULATOR - SKEUOMORPHIC CSS
   Premium Apple-style Design
   ============================================ */

/* ── CSS Custom Properties (Light Theme) ── */
:root {
    /* Body */
    --body-bg: linear-gradient(135deg, #667eea 0%, #764ba2 100%);

    /* Calculator Body */
    --calc-bg: linear-gradient(160deg, #e8e8e8 0%, #d4d4d4 40%, #c8c8c8 100%);
    --calc-shadow: 
        0 25px 60px rgba(0, 0, 0, 0.35),
        0 0 0 1px rgba(255, 255, 255, 0.4);
    --calc-border: 1px solid #b8b8b8;
    --calc-inner-highlight: inset 0 2px 0 rgba(255, 255, 255, 0.7);

    /* Display */
    --display-bg: linear-gradient(180deg, #1a1a2e 0%, #0d0d1a 100%);
    --display-shadow: 
        inset 0 5px 18px rgba(0, 0, 0, 0.55),
        inset 0 -3px 10px rgba(255, 255, 255, 0.03),
        0 1px 0 rgba(255, 255, 255, 0.15);
    --display-border: 2px solid #2a2a3e;
    --display-text-color: #00e676;
    --display-expr-color: rgba(128, 203, 196, 0.8);
    --display-mode-color: rgba(128, 203, 196, 0.4);

    /* Number Buttons */
    --btn-num-bg: linear-gradient(160deg, #f8f8f8 0%, #e0e0e0 100%);
    --btn-num-shadow: 
        0 4px 8px rgba(0, 0, 0, 0.12),
        0 1px 3px rgba(0, 0, 0, 0.08),
        inset 0 1px 0 rgba(255, 255, 255, 0.9);
    --btn-num-active-shadow: 
        inset 0 2px 6px rgba(0, 0, 0, 0.25),
        inset 0 -1px 2px rgba(255, 255, 255, 0.1);
    --btn-num-color: #333;
    --btn-num-hover: linear-gradient(160deg, #ffffff 0%, #eaeaea 100%);

    /* Operator Buttons */
    --btn-op-bg: linear-gradient(160deg, #c2d9f7 0%, #8ab4f8 100%);
    --btn-op-shadow: 
        0 4px 8px rgba(0, 0, 0, 0.12),
        0 1px 3px rgba(0, 0, 0, 0.08),
        inset 0 1px 0 rgba(255, 255, 255, 0.6);
    --btn-op-active-shadow: 
        inset 0 2px 6px rgba(0, 0, 0, 0.25),
        inset 0 -1px 2px rgba(255, 255, 255, 0.1);
    --btn-op-color: #1a3a6a;
    --btn-op-hover: linear-gradient(160deg, #d4e5ff 0%, #9cc4ff 100%);

    /* Scientific Buttons */
    --btn-sci-bg: linear-gradient(160deg, #e8e8e8 0%, #cfcfcf 100%);
    --btn-sci-shadow: 
        0 3px 6px rgba(0, 0, 0, 0.1),
        inset 0 1px 0 rgba(255, 255, 255, 0.8);
    --btn-sci-active-shadow: 
        inset 0 2px 5px rgba(0, 0, 0, 0.2);
    --btn-sci-color: #555;
    --btn-sci-hover: linear-gradient(160deg, #f0f0f0 0%, #d8d8d8 100%);

    /* Function Buttons (C, ⌫) */
    --btn-func-bg: linear-gradient(160deg, #ffe4bc 0%, #f5c67a 100%);
    --btn-func-shadow: 
        0 4px 8px rgba(0, 0, 0, 0.12),
        inset 0 1px 0 rgba(255, 255, 255, 0.7);
    --btn-func-active-shadow: 
        inset 0 2px 6px rgba(0, 0, 0, 0.2);
    --btn-func-color: #6a4a10;
    --btn-func-hover: linear-gradient(160deg, #fff0d4 0%, #ffd48a 100%);

    /* Equals Button */
    --btn-eq-bg: linear-gradient(160deg, #ffb347 0%, #ff8c00 100%);
    --btn-eq-shadow: 
        0 4px 12px rgba(255, 140, 0, 0.3),
        0 2px 4px rgba(0, 0, 0, 0.15),
        inset 0 1px 0 rgba(255, 255, 255, 0.4);
    --btn-eq-active-shadow: 
        inset 0 2px 8px rgba(0, 0, 0, 0.3);
    --btn-eq-color: #fff;
    --btn-eq-hover: linear-gradient(160deg, #ffc469 0%, #ffa020 100%);

    /* Header */
    --header-color: #888;
    --toggle-bg: rgba(0, 0, 0, 0.06);
    --toggle-hover-bg: rgba(0, 0, 0, 0.12);
}

/* ── Dark Theme Overrides ── */
body.dark {
    --body-bg: linear-gradient(135deg, #1a1a2e 0%, #16213e 100%);

    --calc-bg: linear-gradient(160deg, #2e2e42 0%, #22223a 40%, #1c1c32 100%);
    --calc-shadow: 
        0 25px 60px rgba(0, 0, 0, 0.6),
        0 0 0 1px rgba(255, 255, 255, 0.08);
    --calc-border: 1px solid #444460;
    --calc-inner-highlight: inset 0 2px 0 rgba(255, 255, 255, 0.08);

    --display-bg: linear-gradient(180deg, #0a0a18 0%, #050510 100%);
    --display-shadow: 
        inset 0 5px 18px rgba(0, 0, 0, 0.7),
        inset 0 -3px 10px rgba(255, 255, 255, 0.02),
        0 1px 0 rgba(255, 255, 255, 0.05);
    --display-border: 2px solid #1a1a30;

    --btn-num-bg: linear-gradient(160deg, #3a3a50 0%, #2a2a40 100%);
    --btn-num-shadow: 
        0 4px 8px rgba(0, 0, 0, 0.4),
        inset 0 1px 0 rgba(255, 255, 255, 0.08);
    --btn-num-active-shadow: 
        inset 0 2px 6px rgba(0, 0, 0, 0.5);
    --btn-num-color: #ddd;
    --btn-num-hover: linear-gradient(160deg, #444458 0%, #33334a 100%);

    --btn-op-bg: linear-gradient(160deg, #2a4a80 0%, #1a3a68 100%);
    --btn-op-shadow: 
        0 4px 8px rgba(0, 0, 0, 0.4),
        inset 0 1px 0 rgba(255, 255, 255, 0.1);
    --btn-op-active-shadow: 
        inset 0 2px 6px rgba(0, 0, 0, 0.5);
    --btn-op-color: #a0c4ff;
    --btn-op-hover: linear-gradient(160deg, #345890 0%, #224878 100%);

    --btn-sci-bg: linear-gradient(160deg, #353550 0%, #282840 100%);
    --btn-sci-shadow: 
        0 3px 6px rgba(0, 0, 0, 0.3),
        inset 0 1px 0 rgba(255, 255, 255, 0.06);
    --btn-sci-active-shadow: 
        inset 0 2px 5px rgba(0, 0, 0, 0.4);
    --btn-sci-color: #aaa;
    --btn-sci-hover: linear-gradient(160deg, #3e3e58 0%, #303048 100%);

    --btn-func-bg: linear-gradient(160deg, #5a4820 0%, #4a3818 100%);
    --btn-func-shadow: 
        0 4px 8px rgba(0, 0, 0, 0.4),
        inset 0 1px 0 rgba(255, 255, 255, 0.08);
    --btn-func-active-shadow: 
        inset 0 2px 6px rgba(0, 0, 0, 0.5);
    --btn-func-color: #ffd080;
    --btn-func-hover: linear-gradient(160deg, #6a5828 0%, #5a4820 100%);

    --btn-eq-bg: linear-gradient(160deg, #e08020 0%, #c06800 100%);
    --btn-eq-shadow: 
        0 4px 12px rgba(200, 100, 0, 0.25),
        0 2px 4px rgba(0, 0, 0, 0.3),
        inset 0 1px 0 rgba(255, 255, 255, 0.15);
    --btn-eq-active-shadow: 
        inset 0 2px 8px rgba(0, 0, 0, 0.5);
    --btn-eq-color: #fff;
    --btn-eq-hover: linear-gradient(160deg, #f09030 0%, #d07810 100%);

    --header-color: #777;
    --toggle-bg: rgba(255, 255, 255, 0.08);
    --toggle-hover-bg: rgba(255, 255, 255, 0.15);
}


/* ─────────────────────────────────────────────
   GLOBAL RESET & BASE
   ───────────────────────────────────────────── */

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

html {
    font-size: 16px;
    -webkit-tap-highlight-color: transparent;
}

body {
    min-height: 100vh;
    display: flex;
    justify-content: center;
    align-items: center;
    background: var(--body-bg);
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;
    padding: 20px;
    transition: background 0.4s ease;
}


/* ─────────────────────────────────────────────
   CALCULATOR BODY
   ───────────────────────────────────────────── */

.calculator {
    width: 100%;
    max-width: 380px;
    background: var(--calc-bg);
    border-radius: 32px;
    padding: 20px;
    border: var(--calc-border);
    box-shadow: var(--calc-shadow), var(--calc-inner-highlight);
    position: relative;
    transition: all 0.4s ease;
    /* Prevent text selection on buttons */
    user-select: none;
    -webkit-user-select: none;
}

/* Metallic top highlight strip */
.calculator::before {
    content: '';
    position: absolute;
    top: 0;
    left: 30px;
    right: 30px;
    height: 1px;
    background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.7), transparent);
    border-radius: 50%;
    z-index: 1;
    transition: background 0.4s ease;
}

body.dark .calculator::before {
    background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.15), transparent);
}

/* Subtle bottom reflection */
.calculator::after {
    content: '';
    position: absolute;
    bottom: 0;
    left: 30px;
    right: 30px;
    height: 1px;
    background: linear-gradient(90deg, transparent, rgba(0, 0, 0, 0.08), transparent);
    border-radius: 50%;
}


/* ─────────────────────────────────────────────
   CALCULATOR HEADER
   ───────────────────────────────────────────── */

.calc-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 12px;
    padding: 0 5px;
}

.calc-title {
    font-size: 12px;
    font-weight: 500;
    color: var(--header-color);
    letter-spacing: 1px;
    text-transform: uppercase;
    transition: color 0.4s ease;
}

.toggles {
    display: flex;
    gap: 6px;
}

.toggle-btn {
    width: 34px;
    height: 34px;
    border-radius: 50%;
    border: none;
    background: var(--toggle-bg);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.25s ease;
    box-shadow: 
        0 2px 4px rgba(0, 0, 0, 0.06),
        inset 0 1px 0 rgba(255, 255, 255, 0.3);
}

.toggle-btn:hover {
    background: var(--toggle-hover-bg);
    transform: scale(1.05);
}

.toggle-btn:active {
    transform: scale(0.95);
    box-shadow: inset 0 2px 4px rgba(0, 0, 0, 0.1);
}

.toggle-icon {
    font-size: 15px;
    line-height: 1;
}


/* ─────────────────────────────────────────────
   LCD DISPLAY SCREEN
   ───────────────────────────────────────────── */

.display {
    background: var(--display-bg);
    border-radius: 16px;
    padding: 18px 20px 16px;
    margin-bottom: 16px;
    box-shadow: var(--display-shadow);
    border: var(--display-border);
    position: relative;
    overflow: hidden;
    min-height: 100px;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    transition: all 0.4s ease;
}

/* LCD scanline effect */
.display::after {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background: repeating-linear-gradient(
        0deg,
        transparent,
        transparent 2px,
        rgba(0, 0, 0, 0.025) 2px,
        rgba(0, 0, 0, 0.025) 4px
    );
    pointer-events: none;
    border-radius: 16px;
}

/* Expression line (top, smaller) */
.expression {
    font-family: 'SF Mono', 'Menlo', 'Consolas', 'Courier New', monospace;
    font-size: 16px;
    color: var(--display-expr-color);
    text-align: right;
    min-height: 22px;
    word-wrap: break-word;
    line-height: 1.4;
    transition: color 0.4s ease, font-size 0.2s ease;
    position: relative;
    z-index: 1;
}

/* Result line (bottom, larger) */
.result {
    font-family: 'SF Mono', 'Menlo', 'Consolas', 'Courier New', monospace;
    font-size: 38px;
    font-weight: 600;
    color: var(--display-text-color);
    text-align: right;
    line-height: 1.2;
    margin-top: 4px;
    word-wrap: break-word;
    transition: color 0.4s ease, font-size 0.2s ease;
    position: relative;
    z-index: 1;
    /* Text glow effect */
    text-shadow: 0 0 12px rgba(0, 230, 118, 0.25);
}

body.dark .result {
    text-shadow: 0 0 18px rgba(0, 230, 118, 0.35);
}

/* Result when showing error */
.result.error {
    color: #ff5252;
    text-shadow: 0 0 12px rgba(255, 82, 82, 0.3);
    font-size: 26px;
}

/* Result when it's a live preview */
.result.preview {
    opacity: 0.5;
}

/* Mode indicator (DEG/RAD) */
.mode-indicator {
    position: absolute;
    top: 8px;
    left: 14px;
    font-family: 'SF Mono', 'Menlo', 'Consolas', monospace;
    font-size: 9px;
    color: var(--display-mode-color);
    letter-spacing: 1px;
    font-weight: 600;
    z-index: 2;
}


/* ─────────────────────────────────────────────
   BUTTON GRID
   ───────────────────────────────────────────── */

.button-grid {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
}


/* ─────────────────────────────────────────────
   BASE BUTTON STYLES
   ───────────────────────────────────────────── */

.btn {
    height: 52px;
    border: none;
    border-radius: 14px;
    font-family: inherit;
    font-size: 18px;
    font-weight: 500;
    cursor: pointer;
    position: relative;
    overflow: hidden;
    transition: all 0.18s ease;
    outline: none;

    /* Remove default tap highlight on mobile */
    -webkit-tap-highlight-color: transparent;
}

/* Subtle highlight on top of every button */
.btn::before {
    content: '';
    position: absolute;
    top: 0;
    left: 10%;
    right: 10%;
    height: 50%;
    background: linear-gradient(180deg, rgba(255,255,255,0.15) 0%, transparent 100%);
    border-radius: 14px 14px 50% 50%;
    pointer-events: none;
    transition: opacity 0.18s ease;
}

/* Focus outline for accessibility */
.btn:focus-visible {
    outline: 2px solid #4a90d9;
    outline-offset: 2px;
}


/* ── Number Buttons ── */
.btn.num {
    background: var(--btn-num-bg);
    color: var(--btn-num-color);
    box-shadow: var(--btn-num-shadow);
}

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

.btn.num:active {
    box-shadow: var(--btn-num-active-shadow);
    transform: translateY(1px);
}

.btn.num:active::before {
    opacity: 0;
}


/* ── Zero Button (spans 2 columns) ── */
.btn.zero {
    grid-column: span 2;
}


/* ── Operator Buttons ── */
.btn.op {
    background: var(--btn-op-bg);
    color: var(--btn-op-color);
    box-shadow: var(--btn-op-shadow);
    font-weight: 600;
}

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

.btn.op:active {
    box-shadow: var(--btn-op-active-shadow);
    transform: translateY(1px);
}

.btn.op:active::before {
    opacity: 0;
}


/* ── Scientific Function Buttons ── */
.btn.sci {
    background: var(--btn-sci-bg);
    color: var(--btn-sci-color);
    box-shadow: var(--btn-sci-shadow);
    font-size: 15px;
    height: 46px;
    border-radius: 12px;
}

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

.btn.sci:active {
    box-shadow: var(--btn-sci-active-shadow);
    transform: translateY(1px);
}

.btn.sci:active::before {
    opacity: 0;
}


/* ── Function Buttons (C, ⌫) ── */
.btn.func {
    background: var(--btn-func-bg);
    color: var(--btn-func-color);
    box-shadow: var(--btn-func-shadow);
    font-weight: 600;
}

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

.btn.func:active {
    box-shadow: var(--btn-func-active-shadow);
    transform: translateY(1px);
}

.btn.func:active::before {
    opacity: 0;
}


/* ── Equals Button ── */
.btn.equals {
    grid-column: span 4;
    background: var(--btn-eq-bg);
    color: var(--btn-eq-color);
    box-shadow: var(--btn-eq-shadow);
    font-size: 22px;
    font-weight: 700;
    height: 52px;
    letter-spacing: 2px;
}

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

.btn.equals:active {
    box-shadow: var(--btn-eq-active-shadow);
    transform: translateY(1px);
}

.btn.equals:active::before {
    opacity: 0;
}


/* ─────────────────────────────────────────────
   BUTTON PRESS ANIMATION
   ───────────────────────────────────────────── */

@keyframes btnPress {
    0%   { transform: scale(1); }
    50%  { transform: scale(0.95) translateY(1px); }
    100% { transform: scale(1); }
}

.btn.pressing {
    animation: btnPress 0.15s ease;
}


/* ─────────────────────────────────────────────
   RESULT FLASH ANIMATION
   ───────────────────────────────────────────── */

@keyframes resultFlash {
    0%   { text-shadow: 0 0 12px rgba(0, 230, 118, 0.25); }
    50%  { text-shadow: 0 0 30px rgba(0, 230, 118, 0.6); }
    100% { text-shadow: 0 0 12px rgba(0, 230, 118, 0.25); }
}

.result.flash {
    animation: resultFlash 0.4s ease;
}


/* ─────────────────────────────────────────────
   ERROR SHAKE ANIMATION
   ───────────────────────────────────────────── */

@keyframes shake {
    0%, 100% { transform: translateX(0); }
    20%      { transform: translateX(-6px); }
    40%      { transform: translateX(6px); }
    60%      { transform: translateX(-4px); }
    80%      { transform: translateX(4px); }
}

.display.shake {
    animation: shake 0.35s ease;
}


/* ─────────────────────────────────────────────
   RESPONSIVE DESIGN
   ───────────────────────────────────────────── */

/* Large phones */
@media (max-width: 420px) {
    .calculator {
        max-width: 340px;
        padding: 16px;
        border-radius: 28px;
    }

    .display {
        padding: 14px 16px 12px;
        min-height: 90px;
        border-radius: 14px;
    }

    .result {
        font-size: 34px;
    }

    .expression {
        font-size: 14px;
    }

    .btn {
        height: 48px;
        font-size: 17px;
        border-radius: 12px;
    }

    .btn.sci {
        height: 42px;
        font-size: 14px;
        border-radius: 10px;
    }

    .btn.equals {
        height: 48px;
        font-size: 20px;
    }

    .button-grid {
        gap: 8px;
    }
}

/* Very small screens */
@media (max-width: 350px) {
    body {
        padding: 10px;
    }

    .calculator {
        max-width: 300px;
        padding: 12px;
        border-radius: 24px;
    }

    .display {
        min-height: 80px;
        padding: 12px 14px 10px;
    }

    .result {
        font-size: 28px;
    }

    .expression {
        font-size: 13px;
    }

    .btn {
        height: 42px;
        font-size: 15px;
        border-radius: 10px;
    }

    .btn.sci {
        height: 38px;
        font-size: 13px;
    }

    .btn.equals {
        height: 42px;
        font-size: 18px;
    }

    .button-grid {
        gap: 6px;
    }
}

/* Tablets and larger */
@media (min-width: 768px) {
    .calculator {
        max-width: 400px;
        padding: 24px;
    }

    .display {
        min-height: 110px;
    }

    .btn {
        height: 56px;
        font-size: 19px;
    }

    .btn.sci {
        height: 48px;
        font-size: 16px;
    }

    .btn.equals {
        height: 56px;
        font-size: 24px;
    }

    .button-grid {
        gap: 12px;
    }
}