:root {
    --bg-gradient-start: #667eea;
    --bg-gradient-end: #764ba2;
    --calculator-bg: #333;
    --calculator-shadow: rgba(0, 0, 0, 0.3);
    --display-bg: #000;
    --display-text: white;
    --number-bg: #666;
    --number-bg-hover: #777;
    --number-text: white;
    --operator-bg: #ff9500;
    --operator-bg-hover: #ffad33;
    --operator-text: white;
    --clear-bg: #a6a6a6;
    --clear-bg-hover: #b8b8b8;
    --clear-text: black;
    --advanced-bg: #9b59b6;
    --advanced-bg-hover: #8e44ad;
    --advanced-text: white;
    --theme-btn-bg: rgba(255, 255, 255, 0.2);
    --theme-btn-text: white;
}

[data-theme="light"] {
    --bg-gradient-start: #74b9ff;
    --bg-gradient-end: #0984e3;
    --calculator-bg: #fff;
    --calculator-shadow: rgba(0, 0, 0, 0.1);
    --display-bg: #f8f9fa;
    --display-text: #2d3436;
    --number-bg: #e9ecef;
    --number-bg-hover: #dee2e6;
    --number-text: #2d3436;
    --operator-bg: #0984e3;
    --operator-bg-hover: #74b9ff;
    --operator-text: white;
    --clear-bg: #fd79a8;
    --clear-bg-hover: #e84393;
    --clear-text: white;
    --advanced-bg: #6c5ce7;
    --advanced-bg-hover: #5f3dc4;
    --advanced-text: white;
    --theme-btn-bg: rgba(0, 0, 0, 0.1);
    --theme-btn-text: #2d3436;
}

[data-theme="neon"] {
    --bg-gradient-start: #1a1a2e;
    --bg-gradient-end: #16213e;
    --calculator-bg: #0f0f0f;
    --calculator-shadow: 0 0 20px #00ffff;
    --display-bg: #000;
    --display-text: #00ffff;
    --number-bg: #2d2d2d;
    --number-bg-hover: #3d3d3d;
    --number-text: #00ffff;
    --operator-bg: #ff0080;
    --operator-bg-hover: #ff3399;
    --operator-text: white;
    --clear-bg: #ff6b35;
    --clear-bg-hover: #ff8c42;
    --clear-text: white;
    --advanced-bg: #9013fe;
    --advanced-bg-hover: #7209b7;
    --advanced-text: white;
    --theme-btn-bg: rgba(0, 255, 255, 0.2);
    --theme-btn-text: #00ffff;
}

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

/* Mobile optimizations */
html, body {
    -webkit-text-size-adjust: 100%;
    -webkit-tap-highlight-color: transparent;
    -webkit-touch-callout: none;
    -webkit-user-select: none;
    -moz-user-select: none;
    -ms-user-select: none;
    user-select: none;
    overscroll-behavior: none;
}

body {
    font-family: Arial, sans-serif;
    background: linear-gradient(135deg, var(--bg-gradient-start) 0%, var(--bg-gradient-end) 100%);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    transition: all 0.3s ease;
}

.controls {
    position: absolute;
    top: 20px;
    right: 20px;
    display: flex;
    gap: 10px;
}

#theme-toggle, #sound-toggle {
    background: var(--theme-btn-bg);
    color: var(--theme-btn-text);
    border: 2px solid var(--theme-btn-text);
    border-radius: 50%;
    width: 50px;
    height: 50px;
    font-size: 20px;
    cursor: pointer;
    transition: all 0.3s ease;
    backdrop-filter: blur(10px);
}

#theme-toggle:hover {
    transform: rotate(180deg) scale(1.1);
    box-shadow: 0 0 15px var(--theme-btn-text);
}

#sound-toggle:hover {
    transform: scale(1.1);
    box-shadow: 0 0 15px var(--theme-btn-text);
}

#sound-toggle:active {
    transform: scale(0.9);
}

.calculator {
    background: var(--calculator-bg);
    border-radius: 20px;
    padding: 20px;
    box-shadow: 0 10px 30px var(--calculator-shadow);
    width: 350px;
    transition: all 0.3s ease;
}

.display {
    margin-bottom: 15px;
}

#display {
    width: 100%;
    height: 60px;
    background: var(--display-bg);
    color: var(--display-text);
    font-size: 24px;
    text-align: right;
    padding: 0 15px;
    border: none;
    border-radius: 10px;
    outline: none;
    transition: all 0.3s ease;
    -webkit-tap-highlight-color: transparent;
    -webkit-user-select: none;
    user-select: none;
    touch-action: none;
}

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

.btn {
    height: 60px;
    border: none;
    border-radius: 10px;
    font-size: 18px;
    font-weight: bold;
    cursor: pointer;
    transition: transform 0.05s ease-out;
    -webkit-tap-highlight-color: transparent;
    -webkit-touch-callout: none;
    -webkit-user-select: none;
    touch-action: manipulation;
    min-height: 44px; /* iOS accessibility minimum */
}

.btn:hover {
    transform: scale(0.95);
}

.btn:active {
    transform: scale(0.9);
}

.number {
    background: var(--number-bg);
    color: var(--number-text);
    transition: background-color 0.1s ease;
}

.operator {
    background: var(--operator-bg);
    color: var(--operator-text);
    transition: background-color 0.1s ease;
}

.clear {
    background: var(--clear-bg);
    color: var(--clear-text);
    transition: background-color 0.1s ease;
}

.equals {
    background: var(--operator-bg);
    color: var(--operator-text);
    grid-row: span 2;
    height: 130px;
    transition: background-color 0.1s ease;
}

.advanced {
    background: var(--advanced-bg);
    color: var(--advanced-text);
    transition: background-color 0.1s ease;
}

/* Only apply hover color changes on non-touch devices */
@media (hover: hover) {
    .number:hover {
        background: var(--number-bg-hover);
    }
    
    .operator:hover {
        background: var(--operator-bg-hover);
    }
    
    .clear:hover {
        background: var(--clear-bg-hover);
    }
    
    .equals:hover {
        background: var(--operator-bg-hover);
    }
    
    .advanced:hover {
        background: var(--advanced-bg-hover);
    }
}

.zero {
    grid-column: span 2;
}

/* Fun animations */
@keyframes shake {
    0%, 100% { transform: translateX(0); }
    10%, 30%, 50%, 70%, 90% { transform: translateX(-5px); }
    20%, 40%, 60%, 80% { transform: translateX(5px); }
}

@keyframes pulse {
    0% { transform: scale(1); }
    50% { transform: scale(1.02); }
    100% { transform: scale(1); }
}

@keyframes bounce {
    0%, 100% { transform: scale(1); }
    50% { transform: scale(1.05); }
}

.btn:active {
    transform: scale(0.95);
}

/* Only apply hover effects on non-touch devices */
@media (hover: hover) {
    .btn:hover {
        transform: translateY(-2px);
        box-shadow: 0 4px 15px rgba(0,0,0,0.3);
        transition: all 0.15s ease;
    }
    
    .equals:hover {
        animation: pulse 1s infinite;
    }
    
    .advanced:hover {
        transform: translateY(-2px) rotate(5deg);
    }
}

/* Disable animations on touch devices for better performance */
@media (hover: none) {
    .btn {
        transition: transform 0.05s ease;
    }
    
    .btn:hover {
        transform: none;
        box-shadow: none;
    }
    
    .equals:hover {
        animation: none;
    }
    
    .advanced:hover {
        transform: none;
    }
}

/* Mobile responsive design */
@media (max-width: 480px) {
    body {
        padding: 10px;
        justify-content: flex-start;
        padding-top: 60px;
    }
    
    .calculator {
        width: 100%;
        max-width: 400px;
        margin: 0 auto;
    }
    
    .controls {
        top: 10px;
        right: 10px;
    }
    
    #theme-toggle, #sound-toggle {
        width: 45px;
        height: 45px;
        font-size: 18px;
    }
    
    .btn {
        height: 70px;
        font-size: 20px;
        min-height: 48px;
    }
    
    #display {
        height: 70px;
        font-size: 28px;
        padding: 0 20px;
    }
    
    .buttons {
        gap: 12px;
    }
    
    .equals {
        height: 152px;
    }
}

@media (max-width: 360px) {
    .calculator {
        width: calc(100vw - 20px);
        padding: 15px;
    }
    
    .btn {
        height: 65px;
        font-size: 18px;
    }
    
    #display {
        height: 65px;
        font-size: 26px;
    }
    
    .equals {
        height: 142px;
    }
}

/* Landscape mobile optimization */
@media (max-height: 600px) and (orientation: landscape) {
    body {
        padding-top: 10px;
        align-items: flex-start;
        justify-content: center;
    }
    
    .calculator {
        margin-top: 10px;
    }
    
    .controls {
        top: 5px;
        right: 5px;
    }
    
    .btn {
        height: 50px;
        font-size: 16px;
    }
    
    #display {
        height: 50px;
        font-size: 22px;
    }
    
    .equals {
        height: 112px;
    }
}

/* Prevent zoom on double tap */
button, input {
    touch-action: manipulation;
}

/* Hide native browser controls on mobile */
@media (max-width: 768px) {
    body {
        -webkit-user-select: none;
        -webkit-touch-callout: none;
    }
}