/* Advanced Calculator Styles */
:root {
    --primary-color: #2563eb;
    --primary-dark: #1d4ed8;
    --primary-light: #60a5fa;
    --secondary-color: #7c3aed;
    --accent-color: #06b6d4;
    --success-color: #10b981;
    --warning-color: #f59e0b;
    --error-color: #ef4444;
    
    --background: #ffffff;
    --surface: #f8fafc;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --border-color: #e2e8f0;
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.1);
    --shadow-lg: 0 20px 25px -5px rgba(0, 0, 0, 0.1);
    --shadow-xl: 0 25px 50px -12px rgba(0, 0, 0, 0.25);
}

[data-theme="dark"] {
    --background: #0f172a;
    --surface: #1e293b;
    --text-primary: #f8fafc;
    --text-secondary: #94a3b8;
    --border-color: #334155;
    --shadow: 0 4px 6px -1px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 20px 25px -5px rgba(0, 0, 0, 0.3);
    --shadow-xl: 0 25px 50px -12px rgba(0, 0, 0, 0.4);
}

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

body {
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, var(--background), var(--surface));
    color: var(--text-primary);
    min-height: 100vh;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all 0.3s ease;
    overflow-x: hidden;
}

.calculator-container {
    display: flex;
    gap: 2rem;
    align-items: flex-start;
    max-width: 1200px;
    margin: 0 auto;
    padding: 2rem;
}

.calculator {
    background: var(--surface);
    border-radius: 25px;
    box-shadow: var(--shadow-xl);
    padding: 2.5rem;
    width: 420px;
    border: 1px solid var(--border-color);
    transition: all 0.3s ease;
    position: relative;
    overflow: hidden;
}

.calculator::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 3px;
    background: linear-gradient(90deg, var(--primary-color), var(--secondary-color), var(--accent-color));
    border-radius: 25px 25px 0 0;
}

.calculator-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2.5rem;
}

.calculator-header h1 {
    font-size: 1.6rem;
    font-weight: 700;
    color: var(--text-primary);
    display: flex;
    align-items: center;
    gap: 0.8rem;
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    -webkit-background-clip: text;
    background-clip: text;
    -webkit-text-fill-color: transparent;
}

.theme-toggle {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    width: 45px;
    height: 45px;
    border-radius: 50%;
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
    transition: all 0.3s ease;
    box-shadow: var(--shadow);
}

.theme-toggle:hover {
    transform: scale(1.1) rotate(180deg);
    box-shadow: var(--shadow-lg);
}

.display {
    background: var(--background);
    border-radius: 20px;
    padding: 2rem;
    margin-bottom: 2.5rem;
    border: 2px solid var(--border-color);
    min-height: 120px;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
    position: relative;
    overflow: hidden;
}

.display::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 2px;
    background: linear-gradient(90deg, var(--primary-color), var(--secondary-color));
}

.previous-operand {
    color: var(--text-secondary);
    font-size: 1.1rem;
    margin-bottom: 0.8rem;
    min-height: 1.8rem;
    text-align: right;
    font-weight: 500;
}

.current-operand {
    color: var(--text-primary);
    font-size: 3rem;
    font-weight: 700;
    text-align: right;
    word-wrap: break-word;
    word-break: break-all;
    line-height: 1.2;
}

.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 1.2rem;
    margin-bottom: 2.5rem;
}

.btn {
    background: var(--background);
    border: 2px solid var(--border-color);
    border-radius: 15px;
    padding: 1.5rem;
    font-size: 1.3rem;
    font-weight: 600;
    color: var(--text-primary);
    cursor: pointer;
    transition: all 0.3s cubic-bezier(0.4, 0, 0.2, 1);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.5rem;
    min-height: 70px;
    position: relative;
    overflow: hidden;
}

.btn::before {
    content: '';
    position: absolute;
    top: 0;
    left: -100%;
    width: 100%;
    height: 100%;
    background: linear-gradient(90deg, transparent, rgba(255, 255, 255, 0.2), transparent);
    transition: left 0.5s ease;
}

.btn:hover::before {
    left: 100%;
}

.btn:hover {
    transform: translateY(-3px);
    box-shadow: var(--shadow-lg);
}

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

.btn.number {
    background: linear-gradient(135deg, var(--surface), var(--background));
    border-color: var(--border-color);
}

.btn.number:hover {
    background: linear-gradient(135deg, var(--primary-light), var(--primary-color));
    color: white;
    border-color: var(--primary-color);
}

.btn.operator {
    background: linear-gradient(135deg, var(--accent-color), var(--primary-color));
    color: white;
    border-color: var(--accent-color);
}

.btn.operator:hover {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    border-color: var(--primary-color);
    transform: translateY(-3px) scale(1.05);
}

.btn.clear {
    background: linear-gradient(135deg, var(--error-color), #dc2626);
    color: white;
    border-color: var(--error-color);
}

.btn.clear:hover {
    background: linear-gradient(135deg, #dc2626, #b91c1c);
    transform: translateY(-3px) scale(1.05);
}

.btn.equals {
    background: linear-gradient(135deg, var(--success-color), #059669);
    color: white;
    grid-column: span 2;
    border-color: var(--success-color);
}

.btn.equals:hover {
    background: linear-gradient(135deg, #059669, #047857);
    transform: translateY(-3px) scale(1.05);
}

.btn.zero {
    grid-column: span 2;
}

.calculator-footer {
    display: flex;
    gap: 1.2rem;
}

.history-toggle,
.scientific-toggle {
    flex: 1;
    background: linear-gradient(135deg, var(--surface), var(--background));
    border: 2px solid var(--border-color);
    border-radius: 15px;
    padding: 1rem;
    text-align: center;
    cursor: pointer;
    transition: all 0.3s ease;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 0.8rem;
    font-weight: 600;
    font-size: 1rem;
}

.history-toggle:hover,
.scientific-toggle:hover {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    transform: translateY(-3px);
    box-shadow: var(--shadow-lg);
    border-color: var(--primary-color);
}

.history-panel {
    background: var(--surface);
    border-radius: 25px;
    box-shadow: var(--shadow-xl);
    padding: 2.5rem;
    width: 350px;
    border: 1px solid var(--border-color);
    transition: all 0.3s ease;
    max-height: 700px;
    overflow-y: auto;
    position: relative;
}

.history-panel::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    height: 3px;
    background: linear-gradient(90deg, var(--accent-color), var(--success-color));
    border-radius: 25px 25px 0 0;
}

.history-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 2rem;
    padding-bottom: 1.5rem;
    border-bottom: 2px solid var(--border-color);
}

.history-header h3 {
    font-size: 1.4rem;
    font-weight: 700;
    color: var(--text-primary);
    display: flex;
    align-items: center;
    gap: 0.8rem;
}

.clear-history {
    background: linear-gradient(135deg, var(--error-color), #dc2626);
    color: white;
    border: none;
    border-radius: 12px;
    padding: 0.8rem 1.2rem;
    cursor: pointer;
    font-size: 0.9rem;
    font-weight: 600;
    transition: all 0.3s ease;
    display: flex;
    align-items: center;
    gap: 0.5rem;
}

.clear-history:hover {
    background: linear-gradient(135deg, #dc2626, #b91c1c);
    transform: scale(1.05);
}

.history-list {
    display: flex;
    flex-direction: column;
    gap: 1rem;
}

.history-item {
    background: var(--background);
    border: 2px solid var(--border-color);
    border-radius: 15px;
    padding: 1.2rem;
    cursor: pointer;
    transition: all 0.3s ease;
    position: relative;
    overflow: hidden;
}

.history-item::before {
    content: '';
    position: absolute;
    top: 0;
    left: 0;
    width: 4px;
    height: 100%;
    background: linear-gradient(180deg, var(--primary-color), var(--secondary-color));
    transition: width 0.3s ease;
}

.history-item:hover {
    background: linear-gradient(135deg, var(--primary-color), var(--secondary-color));
    color: white;
    transform: translateX(8px);
    border-color: var(--primary-color);
    box-shadow: var(--shadow-lg);
}

.history-item:hover::before {
    width: 100%;
    opacity: 0.1;
}

.history-expression {
    font-size: 1rem;
    color: var(--text-secondary);
    margin-bottom: 0.5rem;
    font-weight: 500;
}

.history-result {
    font-size: 1.3rem;
    font-weight: 700;
    color: var(--text-primary);
}

.history-item:hover .history-expression,
.history-item:hover .history-result {
    color: white;
}

/* Responsive Design */
@media (max-width: 768px) {
    .calculator-container {
        flex-direction: column;
        align-items: center;
        padding: 1rem;
        gap: 1.5rem;
    }
    
    .calculator {
        width: 100%;
        max-width: 400px;
        padding: 2rem;
    }
    
    .history-panel {
        width: 100%;
        max-width: 400px;
        padding: 2rem;
    }
    
    .buttons {
        gap: 1rem;
    }
    
    .btn {
        padding: 1.2rem;
        font-size: 1.2rem;
        min-height: 60px;
    }
    
    .current-operand {
        font-size: 2.5rem;
    }
    
    .calculator-header h1 {
        font-size: 1.4rem;
    }
}

/* Animation for button press */
@keyframes buttonPress {
    0% { transform: scale(1); }
    50% { transform: scale(0.95); }
    100% { transform: scale(1); }
}

.btn:active {
    animation: buttonPress 0.1s ease;
}

/* Smooth transitions */
* {
    transition: background-color 0.3s ease, color 0.3s ease, border-color 0.3s ease;
}

/* Custom scrollbar for history panel */
.history-panel::-webkit-scrollbar {
    width: 8px;
}

.history-panel::-webkit-scrollbar-track {
    background: var(--surface);
    border-radius: 4px;
}

.history-panel::-webkit-scrollbar-thumb {
    background: linear-gradient(180deg, var(--primary-color), var(--secondary-color));
    border-radius: 4px;
}

.history-panel::-webkit-scrollbar-thumb:hover {
    background: linear-gradient(180deg, var(--primary-dark), var(--secondary-color));
}

/* Loading animation */
@keyframes pulse {
    0%, 100% { opacity: 1; }
    50% { opacity: 0.5; }
}

.loading {
    animation: pulse 1.5s ease-in-out infinite;
}