* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
    font-family: 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
}

:root {
    --primary-color: #2563eb;
    --secondary-color: #3b82f6;
    --accent-color: #60a5fa;
    --background-color: #f8fafc;
    --surface-color: #ffffff;
    --text-primary: #1e293b;
    --text-secondary: #64748b;
    --shadow: 0 10px 25px rgba(0, 0, 0, 0.1);
    --border-radius: 16px;
    --tab-active: #2563eb;
    --tab-inactive: #e2e8f0;
}

[data-theme="dark"] {
    --primary-color: #3b82f6;
    --secondary-color: #60a5fa;
    --accent-color: #93c5fd;
    --background-color: #0f172a;
    --surface-color: #1e293b;
    --text-primary: #f1f5f9;
    --text-secondary: #cbd5e1;
    --shadow: 0 10px 25px rgba(0, 0, 0, 0.3);
    --tab-active: #3b82f6;
    --tab-inactive: #334155;
}

body {
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background-color: var(--background-color);
    color: var(--text-primary);
    padding: 20px;
    transition: background-color 0.3s ease, color 0.3s ease;
}

.calculator-container {
    width: 100%;
    max-width: 700px;
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.calculator {
    background-color: var(--surface-color);
    border-radius: var(--border-radius);
    box-shadow: var(--shadow);
    overflow: hidden;
    padding: 25px;
    transition: all 0.3s ease;
}

.header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
}

.title {
    font-size: 1.5rem;
    font-weight: 600;
    color: var(--text-primary);
}

.theme-toggle {
    display: flex;
    align-items: center;
    gap: 8px;
}

.theme-label {
    font-size: 0.8rem;
    color: var(--text-secondary);
}

.switch {
    position: relative;
    display: inline-block;
    width: 50px;
    height: 24px;
}

.switch input {
    opacity: 0;
    width: 0;
    height: 0;
}

.slider {
    position: absolute;
    cursor: pointer;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    background-color: #ccc;
    transition: .4s;
    border-radius: 24px;
}

.slider:before {
    position: absolute;
    content: "";
    height: 16px;
    width: 16px;
    left: 4px;
    bottom: 4px;
    background-color: white;
    transition: .4s;
    border-radius: 50%;
}

input:checked + .slider {
    background-color: var(--primary-color);
}

input:checked + .slider:before {
    transform: translateX(26px);
}

/* Tabs */
.tabs {
    display: flex;
    margin-bottom: 20px;
    border-bottom: 1px solid var(--tab-inactive);
}

.tab-button {
    flex: 1;
    padding: 12px 8px;
    background: none;
    border: none;
    border-bottom: 3px solid transparent;
    color: var(--text-secondary);
    cursor: pointer;
    transition: all 0.3s ease;
    font-weight: 500;
}

.tab-button:hover {
    color: var(--primary-color);
    background-color: rgba(37, 99, 235, 0.1);
}

.tab-button.active {
    color: var(--tab-active);
    border-bottom-color: var(--tab-active);
}

.tab-content {
    display: none;
}

.tab-content.active {
    display: block;
}

.display-container {
    background-color: var(--background-color);
    border-radius: 12px;
    padding: 20px;
    margin-bottom: 20px;
    text-align: right;
    min-height: 120px;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
}

.calculation-display {
    font-size: 1.2rem;
    color: var(--text-secondary);
    margin-bottom: 10px;
    min-height: 1.5rem;
    word-break: break-all;
}

.result-display {
    font-size: 2.5rem;
    font-weight: 600;
    color: var(--text-primary);
    word-break: break-all;
}

/* Basic Calculator Styles */
.buttons {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-gap: 10px;
    margin-bottom: 15px;
}

.btn {
    border: none;
    padding: 15px 8px;
    font-size: 1.1rem;
    border-radius: 10px;
    cursor: pointer;
    transition: all 0.2s ease;
    outline: none;
    font-weight: 500;
    display: flex;
    align-items: center;
    justify-content: center;
    box-shadow: 0 4px 6px rgba(0, 0, 0, 0.05);
}

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

.btn:hover {
    filter: brightness(1.1);
}

.number, .decimal {
    background-color: var(--background-color);
    color: var(--text-primary);
}

.number:hover, .decimal:hover {
    background-color: var(--accent-color);
    color: white;
}

.operator {
    background-color: var(--secondary-color);
    color: white;
}

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

.equals {
    background-color: var(--primary-color);
    color: white;
    grid-column: span 1;
}

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

.clear {
    background-color: #ef4444;
    color: white;
}

.clear:hover {
    background-color: #dc2626;
}

.zero {
    grid-column: span 2;
}

.memory-functions {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-gap: 10px;
    margin-bottom: 15px;
}

.memory {
    background-color: var(--background-color);
    color: var(--text-primary);
    font-size: 0.9rem;
    padding: 12px 5px;
}

.memory:hover {
    background-color: var(--accent-color);
    color: white;
}

/* Scientific Calculator Styles */
.scientific-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    grid-gap: 20px;
}

.scientific-functions {
    display: flex;
    flex-direction: column;
    gap: 8px;
}

.scientific-row {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-gap: 8px;
}

.scientific {
    background-color: var(--background-color);
    color: var(--text-primary);
    font-size: 0.85rem;
    padding: 12px 5px;
}

.scientific:hover {
    background-color: var(--accent-color);
    color: white;
}

.scientific-basic .buttons {
    grid-gap: 8px;
}

.scientific-basic .btn {
    padding: 12px 6px;
    font-size: 1rem;
}

.scientific-basic .memory-functions {
    grid-gap: 8px;
}

.scientific-basic .memory {
    padding: 10px 5px;
    font-size: 0.8rem;
}

/* Statistics Calculator Styles */
.stats-input {
    margin-bottom: 15px;
}

.input-group {
    display: flex;
    gap: 10px;
    margin-bottom: 15px;
}

#data-input {
    flex: 1;
    padding: 12px;
    border: 1px solid var(--tab-inactive);
    border-radius: 8px;
    background-color: var(--background-color);
    color: var(--text-primary);
}

.data-set {
    margin-bottom: 15px;
}

.data-set h3 {
    margin-bottom: 8px;
    font-size: 1rem;
    color: var(--text-secondary);
}

.data-values {
    background-color: var(--background-color);
    padding: 12px;
    border-radius: 8px;
    min-height: 40px;
    font-family: monospace;
}

.stats-buttons {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-gap: 10px;
    margin-bottom: 15px;
}

.stats {
    background-color: var(--background-color);
    color: var(--text-primary);
    font-size: 0.9rem;
    padding: 12px 5px;
}

.stats:hover {
    background-color: var(--accent-color);
    color: white;
}

.stats-results {
    background-color: var(--background-color);
    padding: 15px;
    border-radius: 8px;
    min-height: 60px;
    font-family: monospace;
    white-space: pre-wrap;
}

/* Date Calculator Styles */
.date-inputs {
    display: grid;
    grid-template-columns: 1fr 1fr;
    grid-gap: 15px;
    margin-bottom: 15px;
}

.date-group {
    display: flex;
    flex-direction: column;
    gap: 5px;
}

.date-group label {
    font-size: 0.9rem;
    color: var(--text-secondary);
}

.date-picker {
    padding: 12px;
    border: 1px solid var(--tab-inactive);
    border-radius: 8px;
    background-color: var(--background-color);
    color: var(--text-primary);
}

.date-buttons {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-gap: 10px;
    margin-bottom: 15px;
}

.date {
    background-color: var(--background-color);
    color: var(--text-primary);
    font-size: 0.9rem;
    padding: 12px 5px;
}

.date:hover {
    background-color: var(--accent-color);
    color: white;
}

.date-results {
    background-color: var(--background-color);
    padding: 15px;
    border-radius: 8px;
    min-height: 60px;
    font-family: monospace;
    white-space: pre-wrap;
}

.calculator-info {
    text-align: center;
    font-size: 0.8rem;
    color: var(--text-secondary);
    padding-top: 10px;
    border-top: 1px solid var(--background-color);
}

/* Focus styles for accessibility */
.btn:focus-visible,
input:focus-visible {
    outline: 2px solid var(--primary-color);
    outline-offset: 2px;
}

/* Responsive design */
@media (max-width: 768px) {
    .calculator-container {
        max-width: 100%;
    }
    
    .calculator {
        padding: 15px;
    }
    
    .scientific-grid {
        grid-template-columns: 1fr;
        grid-gap: 15px;
    }
    
    .scientific-row {
        grid-template-columns: repeat(4, 1fr);
    }
    
    .btn {
        padding: 12px 6px;
        font-size: 1rem;
    }
    
    .result-display {
        font-size: 2rem;
    }
    
    .date-inputs {
        grid-template-columns: 1fr;
    }
    
    .stats-buttons,
    .date-buttons {
        grid-template-columns: repeat(2, 1fr);
    }
}

@media (max-width: 480px) {
    .scientific-row {
        grid-template-columns: repeat(3, 1fr);
    }
    
    .scientific {
        font-size: 0.8rem;
        padding: 10px 4px;
    }
    
    .scientific-basic .buttons {
        grid-gap: 6px;
    }
    
    .scientific-basic .btn {
        padding: 10px 4px;
        font-size: 0.9rem;
    }
}

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

.btn.pressed {
    animation: buttonPress 0.2s ease;
}

/* Notification styles */
.notification {
    position: fixed;
    top: 20px;
    right: 20px;
    background: var(--primary-color);
    color: white;
    padding: 12px 18px;
    border-radius: 8px;
    z-index: 1000;
    font-size: 0.9rem;
    box-shadow: var(--shadow);
}