/* ===== CSS Variables & Design System ===== */
:root {
    /* Color Palette - Modern & Vibrant */
    --primary-hue: 250;
    --primary-sat: 85%;
    --primary-light: 60%;
    
    --primary-color: hsl(var(--primary-hue), var(--primary-sat), var(--primary-light));
    --primary-dark: hsl(var(--primary-hue), var(--primary-sat), 50%);
    --primary-light-bg: hsl(var(--primary-hue), var(--primary-sat), 95%);
    
    --accent-color: hsl(320, 85%, 60%);
    --success-color: hsl(150, 70%, 50%);
    --danger-color: hsl(0, 75%, 60%);
    
    /* Dark Mode Colors */
    --bg-primary: hsl(240, 15%, 8%);
    --bg-secondary: hsl(240, 12%, 12%);
    --bg-tertiary: hsl(240, 10%, 16%);
    --bg-hover: hsl(240, 10%, 20%);
    
    --text-primary: hsl(0, 0%, 95%);
    --text-secondary: hsl(0, 0%, 70%);
    --text-muted: hsl(0, 0%, 50%);
    
    /* Glassmorphism */
    --glass-bg: hsla(240, 12%, 15%, 0.7);
    --glass-border: hsla(0, 0%, 100%, 0.1);
    
    /* Shadows */
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.3);
    --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.4);
    --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.5);
    --shadow-glow: 0 0 20px hsla(var(--primary-hue), var(--primary-sat), var(--primary-light), 0.3);
    
    /* Spacing */
    --spacing-xs: 0.5rem;
    --spacing-sm: 0.75rem;
    --spacing-md: 1rem;
    --spacing-lg: 1.5rem;
    --spacing-xl: 2rem;
    --spacing-2xl: 3rem;
    
    /* Border Radius */
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --radius-xl: 24px;
    
    /* Transitions */
    --transition-fast: 150ms ease-in-out;
    --transition-base: 250ms ease-in-out;
    --transition-slow: 400ms ease-in-out;
}

/* ===== Base Styles ===== */
* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, sans-serif;
    background: linear-gradient(135deg, 
        hsl(240, 20%, 10%) 0%, 
        hsl(260, 25%, 8%) 50%, 
        hsl(280, 20%, 10%) 100%);
    background-attachment: fixed;
    color: var(--text-primary);
    line-height: 1.6;
    min-height: 100vh;
    overflow-x: hidden;
}

/* Animated background effect */
body::before {
    content: '';
    position: fixed;
    top: -50%;
    left: -50%;
    width: 200%;
    height: 200%;
    background: radial-gradient(circle, 
        hsla(var(--primary-hue), 80%, 60%, 0.1) 0%, 
        transparent 50%);
    animation: rotate 30s linear infinite;
    pointer-events: none;
    z-index: 0;
}

@keyframes rotate {
    from { transform: rotate(0deg); }
    to { transform: rotate(360deg); }
}

/* ===== Container ===== */
.container {
    max-width: 900px;
    margin: 0 auto;
    padding: var(--spacing-xl) var(--spacing-md);
    position: relative;
    z-index: 1;
}

/* ===== Header ===== */
.header {
    text-align: center;
    margin-bottom: var(--spacing-2xl);
}

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

.app-title {
    font-size: 3.5rem;
    font-weight: 700;
    background: linear-gradient(135deg, 
        var(--primary-color) 0%, 
        var(--accent-color) 100%);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: var(--spacing-sm);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-md);
    animation: fadeInDown 0.6s ease-out;
}

.title-icon {
    font-size: 3rem;
    filter: drop-shadow(0 0 10px var(--primary-color));
}

.app-subtitle {
    color: var(--text-secondary);
    font-size: 1.1rem;
    font-weight: 400;
    animation: fadeInUp 0.6s ease-out 0.1s both;
}

/* ===== Stats Container ===== */
.stats-container {
    display: grid;
    grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
    gap: var(--spacing-md);
    margin-top: var(--spacing-xl);
    animation: fadeInUp 0.6s ease-out 0.2s both;
}

.stat-card {
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-lg);
    padding: var(--spacing-lg);
    text-align: center;
    transition: all var(--transition-base);
}

.stat-card:hover {
    transform: translateY(-4px);
    box-shadow: var(--shadow-md);
    border-color: hsla(0, 0%, 100%, 0.2);
}

.stat-value {
    font-size: 2.5rem;
    font-weight: 700;
    background: linear-gradient(135deg, var(--primary-color), var(--accent-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.stat-label {
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: 500;
    margin-top: var(--spacing-xs);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

/* ===== Main Content ===== */
.main-content {
    background: var(--glass-bg);
    backdrop-filter: blur(20px);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-xl);
    padding: var(--spacing-xl);
    box-shadow: var(--shadow-lg);
    animation: fadeInUp 0.6s ease-out 0.3s both;
}

/* ===== Input Section ===== */
.input-section {
    margin-bottom: var(--spacing-xl);
}

.input-wrapper {
    display: flex;
    gap: var(--spacing-md);
    margin-bottom: var(--spacing-lg);
}

.task-input {
    flex: 1;
    padding: var(--spacing-md) var(--spacing-lg);
    font-size: 1.1rem;
    font-family: inherit;
    background: var(--bg-secondary);
    border: 2px solid transparent;
    border-radius: var(--radius-md);
    color: var(--text-primary);
    transition: all var(--transition-base);
    outline: none;
}

.task-input:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 4px hsla(var(--primary-hue), var(--primary-sat), var(--primary-light), 0.1);
    transform: translateY(-2px);
}

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

.add-btn {
    padding: var(--spacing-md) var(--spacing-xl);
    font-size: 1.1rem;
    font-weight: 600;
    font-family: inherit;
    background: linear-gradient(135deg, var(--primary-color), var(--primary-dark));
    color: white;
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-base);
    display: flex;
    align-items: center;
    gap: var(--spacing-sm);
    box-shadow: var(--shadow-sm);
    position: relative;
    overflow: hidden;
}

.add-btn::before {
    content: '';
    position: absolute;
    top: 50%;
    left: 50%;
    width: 0;
    height: 0;
    border-radius: 50%;
    background: rgba(255, 255, 255, 0.2);
    transform: translate(-50%, -50%);
    transition: width var(--transition-slow), height var(--transition-slow);
}

.add-btn:hover::before {
    width: 300px;
    height: 300px;
}

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

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

.btn-icon {
    font-size: 1.5rem;
    line-height: 1;
}

/* ===== Filter Section ===== */
.filter-section {
    display: flex;
    gap: var(--spacing-sm);
    justify-content: center;
}

.filter-btn {
    padding: var(--spacing-sm) var(--spacing-lg);
    font-size: 0.95rem;
    font-weight: 500;
    font-family: inherit;
    background: var(--bg-secondary);
    color: var(--text-secondary);
    border: 1px solid transparent;
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: all var(--transition-base);
}

.filter-btn:hover {
    background: var(--bg-hover);
    color: var(--text-primary);
}

.filter-btn.active {
    background: linear-gradient(135deg, var(--primary-color), var(--primary-dark));
    color: white;
    border-color: var(--primary-color);
    box-shadow: var(--shadow-sm);
}

/* ===== Tasks Section ===== */
.tasks-section {
    min-height: 300px;
}

.empty-state {
    text-align: center;
    padding: var(--spacing-2xl) var(--spacing-md);
    color: var(--text-muted);
}

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

.empty-state h2 {
    font-size: 1.5rem;
    color: var(--text-secondary);
    margin-bottom: var(--spacing-sm);
}

.empty-state p {
    font-size: 1rem;
}

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

/* ===== Task Item ===== */
.task-item {
    background: var(--bg-secondary);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-md);
    padding: var(--spacing-lg);
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    transition: all var(--transition-base);
    animation: slideIn 0.3s ease-out;
}

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

.task-item:hover {
    background: var(--bg-hover);
    transform: translateX(4px);
    box-shadow: var(--shadow-sm);
}

.task-item.completed {
    opacity: 0.6;
}

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

/* Custom Checkbox */
.task-checkbox {
    width: 24px;
    height: 24px;
    min-width: 24px;
    border: 2px solid var(--text-muted);
    border-radius: 6px;
    cursor: pointer;
    transition: all var(--transition-base);
    position: relative;
    background: transparent;
}

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

.task-item.completed .task-checkbox {
    background: linear-gradient(135deg, var(--success-color), hsl(150, 70%, 40%));
    border-color: var(--success-color);
}

.task-item.completed .task-checkbox::after {
    content: '✓';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    color: white;
    font-size: 14px;
    font-weight: bold;
}

.task-text {
    flex: 1;
    font-size: 1.05rem;
    color: var(--text-primary);
    word-break: break-word;
}

.task-time {
    font-size: 0.85rem;
    color: var(--text-muted);
    white-space: nowrap;
}

.delete-btn {
    padding: var(--spacing-sm) var(--spacing-md);
    font-size: 0.9rem;
    font-weight: 500;
    font-family: inherit;
    background: transparent;
    color: var(--danger-color);
    border: 1px solid var(--danger-color);
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: all var(--transition-base);
    opacity: 0;
}

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

.delete-btn:hover {
    background: var(--danger-color);
    color: white;
    transform: scale(1.05);
}

/* ===== Footer Actions ===== */
.footer-actions {
    margin-top: var(--spacing-xl);
    text-align: center;
}

.clear-btn {
    padding: var(--spacing-md) var(--spacing-xl);
    font-size: 0.95rem;
    font-weight: 500;
    font-family: inherit;
    background: transparent;
    color: var(--text-secondary);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-base);
}

.clear-btn:hover {
    background: var(--danger-color);
    color: white;
    border-color: var(--danger-color);
    transform: translateY(-2px);
    box-shadow: var(--shadow-sm);
}

/* ===== Animations ===== */
@keyframes fadeInDown {
    from {
        opacity: 0;
        transform: translateY(-20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

@keyframes fadeInUp {
    from {
        opacity: 0;
        transform: translateY(20px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

/* ===== Responsive Design ===== */
@media (max-width: 768px) {
    .container {
        padding: var(--spacing-md);
    }
    
    .app-title {
        font-size: 2.5rem;
    }
    
    .title-icon {
        font-size: 2rem;
    }
    
    .input-wrapper {
        flex-direction: column;
    }
    
    .add-btn {
        justify-content: center;
    }
    
    .stats-container {
        grid-template-columns: 1fr;
    }
    
    .task-item {
        flex-wrap: wrap;
    }
    
    .task-time {
        order: 3;
        width: 100%;
        margin-top: var(--spacing-xs);
        margin-left: 40px;
    }
}

@media (max-width: 480px) {
    .app-title {
        font-size: 2rem;
        flex-direction: column;
        gap: var(--spacing-sm);
    }
    
    .main-content {
        padding: var(--spacing-md);
    }
    
    .filter-section {
        flex-direction: column;
    }
    
    .filter-btn {
        width: 100%;
    }
}

/* ===== Authentication Pages ===== */
.auth-container {
    display: flex;
    align-items: center;
    justify-content: center;
    min-height: 100vh;
    padding: var(--spacing-md);
}

.auth-card {
    background: var(--glass-bg);
    backdrop-filter: blur(20px);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-xl);
    padding: var(--spacing-2xl);
    box-shadow: var(--shadow-lg);
    max-width: 450px;
    width: 100%;
    animation: fadeInUp 0.6s ease-out;
}

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

.auth-title {
    font-size: 2.5rem;
    font-weight: 700;
    background: linear-gradient(135deg, var(--primary-color), var(--accent-color));
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
    margin-bottom: var(--spacing-sm);
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
}

.auth-subtitle {
    color: var(--text-secondary);
    font-size: 1rem;
}

.auth-form {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-lg);
}

.form-group {
    display: flex;
    flex-direction: column;
    gap: var(--spacing-xs);
}

.form-label {
    color: var(--text-secondary);
    font-size: 0.9rem;
    font-weight: 500;
}

.form-input {
    padding: var(--spacing-md);
    font-size: 1rem;
    font-family: inherit;
    background: var(--bg-secondary);
    border: 2px solid transparent;
    border-radius: var(--radius-md);
    color: var(--text-primary);
    transition: all var(--transition-base);
    outline: none;
}

.form-input:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 4px hsla(var(--primary-hue), var(--primary-sat), var(--primary-light), 0.1);
}

.error-message {
    padding: var(--spacing-md);
    background: hsla(0, 75%, 60%, 0.1);
    border: 1px solid var(--danger-color);
    border-radius: var(--radius-sm);
    color: var(--danger-color);
    font-size: 0.9rem;
    text-align: center;
}

.auth-btn {
    padding: var(--spacing-md) var(--spacing-xl);
    font-size: 1.1rem;
    font-weight: 600;
    font-family: inherit;
    background: linear-gradient(135deg, var(--primary-color), var(--primary-dark));
    color: white;
    border: none;
    border-radius: var(--radius-md);
    cursor: pointer;
    transition: all var(--transition-base);
    box-shadow: var(--shadow-sm);
}

.auth-btn:hover {
    transform: translateY(-2px);
    box-shadow: var(--shadow-glow);
}

.auth-btn:disabled {
    opacity: 0.6;
    cursor: not-allowed;
    transform: none;
}

.auth-footer {
    text-align: center;
    margin-top: var(--spacing-lg);
    color: var(--text-secondary);
    font-size: 0.9rem;
}

.auth-link {
    color: var(--primary-color);
    text-decoration: none;
    font-weight: 500;
    transition: color var(--transition-fast);
}

.auth-link:hover {
    color: var(--accent-color);
    text-decoration: underline;
}

/* ===== User Profile Section ===== */
.header-top {
    display: flex;
    justify-content: space-between;
    align-items: flex-start;
    margin-bottom: var(--spacing-xl);
    gap: var(--spacing-lg);
}

.user-profile {
    display: flex;
    align-items: center;
    gap: var(--spacing-md);
    background: var(--glass-bg);
    backdrop-filter: blur(10px);
    border: 1px solid var(--glass-border);
    border-radius: var(--radius-lg);
    padding: var(--spacing-md) var(--spacing-lg);
    animation: fadeInDown 0.6s ease-out 0.1s both;
}

.user-info {
    display: flex;
    flex-direction: column;
    align-items: flex-end;
}

.user-name {
    color: var(--text-primary);
    font-weight: 600;
    font-size: 1rem;
}

.user-email {
    color: var(--text-secondary);
    font-size: 0.85rem;
}

.logout-btn {
    padding: var(--spacing-sm) var(--spacing-lg);
    font-size: 0.9rem;
    font-weight: 500;
    font-family: inherit;
    background: transparent;
    color: var(--danger-color);
    border: 1px solid var(--danger-color);
    border-radius: var(--radius-sm);
    cursor: pointer;
    transition: all var(--transition-base);
}

.logout-btn:hover {
    background: var(--danger-color);
    color: white;
    transform: scale(1.05);
}

/* ===== Responsive Updates for Auth ===== */
@media (max-width: 768px) {
    .header-top {
        flex-direction: column;
        align-items: center;
    }
    
    .user-profile {
        width: 100%;
        justify-content: space-between;
    }
    
    .user-info {
        align-items: flex-start;
    }
}