/* ===================================
   CSS RESET & BASE STYLES
   =================================== */

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

/* ===================================
   CSS CUSTOM PROPERTIES (Design Tokens)
   =================================== */

:root {
    /* Colors - Sophisticated Gradient Palette */
    --primary-gradient: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
    --secondary-gradient: linear-gradient(135deg, #f093fb 0%, #f5576c 100%);
    --success-gradient: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
    
    --color-primary: #667eea;
    --color-primary-dark: #5568d3;
    --color-secondary: #764ba2;
    --color-accent: #f5576c;
    --color-success: #00f2fe;
    
    /* Neutrals */
    --color-background: #f8f9fe;
    --color-surface: #ffffff;
    --color-surface-elevated: #ffffff;
    --color-text-primary: #1a1d29;
    --color-text-secondary: #6b7280;
    --color-text-muted: #9ca3af;
    --color-border: #e5e7eb;
    --color-border-light: #f3f4f6;
    
    /* Shadows */
    --shadow-sm: 0 1px 2px 0 rgba(0, 0, 0, 0.05);
    --shadow-md: 0 4px 6px -1px rgba(0, 0, 0, 0.1), 0 2px 4px -1px rgba(0, 0, 0, 0.06);
    --shadow-lg: 0 10px 15px -3px rgba(0, 0, 0, 0.1), 0 4px 6px -2px rgba(0, 0, 0, 0.05);
    --shadow-xl: 0 20px 25px -5px rgba(0, 0, 0, 0.1), 0 10px 10px -5px rgba(0, 0, 0, 0.04);
    --shadow-glow: 0 0 20px rgba(102, 126, 234, 0.3);
    
    /* Typography */
    --font-primary: 'Sora', system-ui, -apple-system, sans-serif;
    --font-mono: 'JetBrains Mono', 'Courier New', monospace;
    
    --font-size-xs: 0.75rem;
    --font-size-sm: 0.875rem;
    --font-size-base: 1rem;
    --font-size-lg: 1.125rem;
    --font-size-xl: 1.25rem;
    --font-size-2xl: 1.5rem;
    --font-size-3xl: 2rem;
    
    --font-weight-light: 300;
    --font-weight-normal: 400;
    --font-weight-semibold: 600;
    --font-weight-bold: 700;
    
    /* Spacing */
    --spacing-xs: 0.25rem;
    --spacing-sm: 0.5rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    
    /* Border Radius */
    --radius-sm: 0.375rem;
    --radius-md: 0.5rem;
    --radius-lg: 0.75rem;
    --radius-xl: 1rem;
    --radius-full: 9999px;
    
    /* Transitions */
    --transition-fast: 150ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-base: 250ms cubic-bezier(0.4, 0, 0.2, 1);
    --transition-slow: 350ms cubic-bezier(0.4, 0, 0.2, 1);
    
    /* Layout */
    --max-width: 720px;
    --header-height: auto;
}

/* ===================================
   GLOBAL STYLES
   =================================== */

html {
    font-size: 16px;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

body {
    font-family: var(--font-primary);
    background: var(--color-background);
    color: var(--color-text-primary);
    line-height: 1.6;
    min-height: 100vh;
    overflow-x: hidden;
}

/* Decorative Background */
body::before {
    content: '';
    position: fixed;
    top: 0;
    left: 0;
    width: 100%;
    height: 100%;
    background: 
        radial-gradient(circle at 20% 30%, rgba(102, 126, 234, 0.08) 0%, transparent 50%),
        radial-gradient(circle at 80% 70%, rgba(118, 75, 162, 0.08) 0%, transparent 50%);
    pointer-events: none;
    z-index: -1;
}

/* ===================================
   CONTAINER & LAYOUT
   =================================== */

.container {
    max-width: var(--max-width);
    margin: 0 auto;
    padding: var(--spacing-lg);
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* ===================================
   HEADER SECTION
   =================================== */

.header {
    margin-bottom: var(--spacing-2xl);
    animation: slideDown 0.6s cubic-bezier(0.16, 1, 0.3, 1);
}

.header-content {
    text-align: center;
    margin-bottom: var(--spacing-xl);
}

.logo-section {
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-sm);
}

.logo-icon {
    width: 50px;
    height: 50px;
    background: var(--primary-gradient);
    color: white;
    border-radius: var(--radius-lg);
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: var(--font-size-2xl);
    font-weight: var(--font-weight-bold);
    box-shadow: var(--shadow-lg);
    animation: float 3s ease-in-out infinite;
}

.app-title {
    font-size: var(--font-size-3xl);
    font-weight: var(--font-weight-bold);
    background: var(--primary-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    letter-spacing: -0.02em;
}

.app-subtitle {
    font-size: var(--font-size-sm);
    color: var(--color-text-secondary);
    font-weight: var(--font-weight-light);
    max-width: 400px;
    margin: 0 auto;
}

/* Stats Bar */
.stats-bar {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    gap: var(--spacing-md);
    background: var(--color-surface);
    padding: var(--spacing-lg);
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-md);
}

.stat-item {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: var(--spacing-xs);
}

.stat-label {
    font-size: var(--font-size-xs);
    color: var(--color-text-muted);
    text-transform: uppercase;
    letter-spacing: 0.05em;
    font-weight: var(--font-weight-semibold);
}

.stat-value {
    font-size: var(--font-size-2xl);
    font-weight: var(--font-weight-bold);
    font-family: var(--font-mono);
    background: var(--primary-gradient);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

/* ===================================
   MAIN CONTENT
   =================================== */

.main-content {
    flex: 1;
}

/* ===================================
   TASK INPUT SECTION
   =================================== */

.task-input-section {
    margin-bottom: var(--spacing-xl);
    animation: slideUp 0.6s cubic-bezier(0.16, 1, 0.3, 1) 0.1s backwards;
}

.task-form {
    width: 100%;
}

.input-wrapper {
    display: flex;
    gap: var(--spacing-md);
    background: var(--color-surface);
    padding: var(--spacing-sm);
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-lg);
    transition: box-shadow var(--transition-base);
}

.input-wrapper:focus-within {
    box-shadow: var(--shadow-xl), var(--shadow-glow);
}

.task-input {
    flex: 1;
    border: none;
    background: transparent;
    font-family: var(--font-primary);
    font-size: var(--font-size-base);
    padding: var(--spacing-md) var(--spacing-lg);
    color: var(--color-text-primary);
    outline: none;
}

.task-input::placeholder {
    color: var(--color-text-muted);
}

.add-button {
    background: var(--primary-gradient);
    color: white;
    border: none;
    padding: var(--spacing-md) var(--spacing-xl);
    border-radius: var(--radius-lg);
    font-family: var(--font-primary);
    font-size: var(--font-size-sm);
    font-weight: var(--font-weight-semibold);
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    transition: all var(--transition-base);
    box-shadow: var(--shadow-md);
}

.add-button:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-lg);
}

.add-button:active {
    transform: translateY(0);
}

.button-icon {
    font-size: var(--font-size-xl);
    font-weight: var(--font-weight-normal);
}

/* ===================================
   FILTER SECTION
   =================================== */

.filter-section {
    margin-bottom: var(--spacing-xl);
    animation: slideUp 0.6s cubic-bezier(0.16, 1, 0.3, 1) 0.2s backwards;
}

.filter-tabs {
    display: flex;
    gap: var(--spacing-sm);
    background: var(--color-surface);
    padding: var(--spacing-sm);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-sm);
}

.filter-tab {
    flex: 1;
    padding: var(--spacing-md) var(--spacing-lg);
    border: none;
    background: transparent;
    color: var(--color-text-secondary);
    font-family: var(--font-primary);
    font-size: var(--font-size-sm);
    font-weight: var(--font-weight-semibold);
    cursor: pointer;
    border-radius: var(--radius-md);
    transition: all var(--transition-base);
}

.filter-tab:hover {
    background: var(--color-border-light);
    color: var(--color-text-primary);
}

.filter-tab.active {
    background: var(--primary-gradient);
    color: white;
    box-shadow: var(--shadow-md);
}

/* ===================================
   TASK LIST SECTION
   =================================== */

.task-list-section {
    margin-bottom: var(--spacing-xl);
    animation: slideUp 0.6s cubic-bezier(0.16, 1, 0.3, 1) 0.3s backwards;
}

/* Empty State */
.empty-state {
    text-align: center;
    padding: var(--spacing-2xl) var(--spacing-lg);
    background: var(--color-surface);
    border-radius: var(--radius-xl);
    box-shadow: var(--shadow-sm);
}

.empty-state.hidden {
    display: none;
}

.empty-icon {
    font-size: 4rem;
    margin-bottom: var(--spacing-md);
    opacity: 0.5;
}

.empty-title {
    font-size: var(--font-size-xl);
    font-weight: var(--font-weight-semibold);
    color: var(--color-text-primary);
    margin-bottom: var(--spacing-sm);
}

.empty-description {
    font-size: var(--font-size-sm);
    color: var(--color-text-secondary);
}

/* Task List */
.task-list {
    list-style: none;
    display: flex;
    flex-direction: column;
    gap: var(--spacing-md);
}

.task-list.hidden {
    display: none;
}

/* Task Item */
.task-item {
    background: var(--color-surface);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    box-shadow: var(--shadow-md);
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    transition: all var(--transition-base);
    animation: slideIn 0.3s cubic-bezier(0.16, 1, 0.3, 1);
    border-left: 4px solid transparent;
}

.task-item:hover {
    transform: translateX(4px);
    box-shadow: var(--shadow-lg);
    border-left-color: var(--color-primary);
}

.task-item.completed {
    opacity: 0.7;
    background: linear-gradient(135deg, rgba(102, 126, 234, 0.05) 0%, rgba(118, 75, 162, 0.05) 100%);
}

.task-item.completed:hover {
    opacity: 0.85;
}

/* Checkbox */
.task-checkbox {
    width: 24px;
    height: 24px;
    min-width: 24px;
    border: 2px solid var(--color-border);
    border-radius: var(--radius-sm);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: all var(--transition-base);
    background: white;
}

.task-checkbox:hover {
    border-color: var(--color-primary);
    transform: scale(1.1);
}

.task-item.completed .task-checkbox {
    background: var(--primary-gradient);
    border-color: var(--color-primary);
}

.task-checkbox::after {
    content: '✓';
    color: white;
    font-size: var(--font-size-sm);
    font-weight: var(--font-weight-bold);
    opacity: 0;
    transform: scale(0);
    transition: all var(--transition-fast);
}

.task-item.completed .task-checkbox::after {
    opacity: 1;
    transform: scale(1);
}

/* Task Text */
.task-text {
    flex: 1;
    font-size: var(--font-size-base);
    color: var(--color-text-primary);
    word-break: break-word;
    transition: all var(--transition-base);
}

.task-item.completed .task-text {
    text-decoration: line-through;
    color: var(--color-text-muted);
}

/* Task Timestamp */
.task-timestamp {
    font-size: var(--font-size-xs);
    color: var(--color-text-muted);
    font-family: var(--font-mono);
    white-space: nowrap;
}

/* Delete Button */
.delete-button {
    background: transparent;
    border: none;
    color: var(--color-text-muted);
    cursor: pointer;
    padding: var(--spacing-sm);
    border-radius: var(--radius-md);
    transition: all var(--transition-base);
    font-size: var(--font-size-lg);
    display: flex;
    align-items: center;
    justify-content: center;
    opacity: 0;
}

.task-item:hover .delete-button {
    opacity: 1;
}

.delete-button:hover {
    background: rgba(245, 87, 108, 0.1);
    color: var(--color-accent);
    transform: scale(1.1);
}

.delete-button:active {
    transform: scale(0.95);
}

/* ===================================
   ACTION BAR
   =================================== */

.action-bar {
    margin-bottom: var(--spacing-xl);
    display: flex;
    justify-content: center;
    animation: slideUp 0.6s cubic-bezier(0.16, 1, 0.3, 1) 0.4s backwards;
}

.action-bar.hidden {
    display: none;
}

.clear-button {
    background: var(--color-surface);
    border: 2px solid var(--color-border);
    color: var(--color-text-secondary);
    padding: var(--spacing-md) var(--spacing-xl);
    border-radius: var(--radius-lg);
    font-family: var(--font-primary);
    font-size: var(--font-size-sm);
    font-weight: var(--font-weight-semibold);
    cursor: pointer;
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    transition: all var(--transition-base);
}

.clear-button:hover {
    background: var(--secondary-gradient);
    color: white;
    border-color: transparent;
    transform: translateY(-2px);
    box-shadow: var(--shadow-md);
}

.clear-button:active {
    transform: translateY(0);
}

.clear-icon {
    font-size: var(--font-size-base);
}

/* ===================================
   FOOTER
   =================================== */

.footer {
    text-align: center;
    padding: var(--spacing-xl) 0;
    margin-top: auto;
    border-top: 1px solid var(--color-border-light);
}

.footer-text {
    font-size: var(--font-size-sm);
    color: var(--color-text-secondary);
    margin-bottom: var(--spacing-xs);
}

.footer-link {
    color: var(--color-primary);
    text-decoration: none;
    font-weight: var(--font-weight-semibold);
    transition: color var(--transition-base);
}

.footer-link:hover {
    color: var(--color-primary-dark);
    text-decoration: underline;
}

.footer-subtitle {
    font-size: var(--font-size-xs);
    color: var(--color-text-muted);
}

/* ===================================
   TOAST NOTIFICATION
   =================================== */

.toast {
    position: fixed;
    bottom: var(--spacing-xl);
    right: var(--spacing-xl);
    background: var(--color-surface-elevated);
    color: var(--color-text-primary);
    padding: var(--spacing-md) var(--spacing-xl);
    border-radius: var(--radius-lg);
    box-shadow: var(--shadow-xl);
    font-size: var(--font-size-sm);
    font-weight: var(--font-weight-semibold);
    transform: translateY(120%);
    opacity: 0;
    transition: all var(--transition-base);
    z-index: 1000;
    max-width: 300px;
    border-left: 4px solid var(--color-primary);
}

.toast.show {
    transform: translateY(0);
    opacity: 1;
}

/* ===================================
   ANIMATIONS
   =================================== */

@keyframes slideDown {
    from {
        opacity: 0;
        transform: translateY(-30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes slideUp {
    from {
        opacity: 0;
        transform: translateY(30px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateX(-20px);
    }
    to {
        opacity: 1;
        transform: translateX(0);
    }
}

@keyframes float {
    0%, 100% {
        transform: translateY(0);
    }
    50% {
        transform: translateY(-5px);
    }
}

/* ===================================
   RESPONSIVE DESIGN
   =================================== */

/* Tablet Devices */
@media (max-width: 768px) {
    :root {
        --font-size-3xl: 1.75rem;
        --font-size-2xl: 1.25rem;
    }
    
    .container {
        padding: var(--spacing-md);
    }
    
    .header {
        margin-bottom: var(--spacing-xl);
    }
    
    .stats-bar {
        padding: var(--spacing-md);
        gap: var(--spacing-sm);
    }
    
    .stat-value {
        font-size: var(--font-size-xl);
    }
    
    .input-wrapper {
        flex-direction: column;
    }
    
    .add-button {
        width: 100%;
        justify-content: center;
    }
    
    .task-item {
        padding: var(--spacing-md);
    }
    
    .delete-button {
        opacity: 1;
    }
}

/* Mobile Devices */
@media (max-width: 480px) {
    :root {
        --font-size-3xl: 1.5rem;
        --spacing-xl: 1.5rem;
        --spacing-2xl: 2rem;
    }
    
    .logo-icon {
        width: 40px;
        height: 40px;
        font-size: var(--font-size-xl);
    }
    
    .app-title {
        font-size: var(--font-size-2xl);
    }
    
    .filter-tabs {
        flex-direction: column;
    }
    
    .filter-tab {
        width: 100%;
    }
    
    .task-timestamp {
        display: none;
    }
    
    .toast {
        right: var(--spacing-md);
        left: var(--spacing-md);
        bottom: var(--spacing-md);
    }
}

/* Accessibility: Reduced Motion */
@media (prefers-reduced-motion: reduce) {
    *,
    *::before,
    *::after {
        animation-duration: 0.01ms !important;
        animation-iteration-count: 1 !important;
        transition-duration: 0.01ms !important;
    }
}

/* Print Styles */
@media print {
    body {
        background: white;
    }
    
    .header,
    .task-input-section,
    .filter-section,
    .action-bar,
    .footer,
    .delete-button {
        display: none;
    }
    
    .task-item {
        box-shadow: none;
        border: 1px solid #000;
        page-break-inside: avoid;
    }
}