/* ===== CSS Variables & Reset ===== */
:root {
    --bg-primary: #0f0f1a;
    --bg-secondary: #1a1a2e;
    --bg-card: #16213e;
    --bg-card-hover: #1a2744;
    --bg-input: #0d1b36;
    --border-color: #2a2a4a;
    --border-focus: #6c63ff;
    --text-primary: #e8e8f0;
    --text-secondary: #9898b0;
    --text-muted: #6868880;
    --accent: #6c63ff;
    --accent-hover: #5a52e0;
    --accent-glow: rgba(108, 99, 255, 0.3);
    --success: #2ecc71;
    --success-bg: rgba(46, 204, 113, 0.12);
    --danger: #e74c3c;
    --danger-hover: #c0392b;
    --warning: #f39c12;
    --gradient-1: linear-gradient(135deg, #6c63ff 0%, #3f8efc 100%);
    --gradient-2: linear-gradient(135deg, #0f0f1a 0%, #1a1a2e 100%);
    --shadow-sm: 0 2px 8px rgba(0, 0, 0, 0.2);
    --shadow-md: 0 4px 16px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 8px 32px rgba(0, 0, 0, 0.4);
    --shadow-glow: 0 0 20px rgba(108, 99, 255, 0.15);
    --radius-sm: 8px;
    --radius-md: 12px;
    --radius-lg: 16px;
    --transition: 0.25s cubic-bezier(0.4, 0, 0.2, 1);
}

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

body {
    font-family: 'Inter', -apple-system, BlinkMacSystemFont, sans-serif;
    background: var(--bg-primary);
    color: var(--text-primary);
    min-height: 100vh;
    line-height: 1.6;
    -webkit-font-smoothing: antialiased;
}

/* ===== App Container ===== */
.app-container {
    max-width: 800px;
    margin: 0 auto;
    padding: 0 20px;
    min-height: 100vh;
    display: flex;
    flex-direction: column;
}

/* ===== Header ===== */
.app-header {
    padding: 32px 0 24px;
    border-bottom: 1px solid var(--border-color);
    margin-bottom: 32px;
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
    gap: 16px;
}

.logo {
    display: flex;
    align-items: center;
    gap: 12px;
}

.logo-icon {
    width: 48px;
    height: 48px;
    background: var(--gradient-1);
    border-radius: var(--radius-md);
    display: flex;
    align-items: center;
    justify-content: center;
    color: white;
    box-shadow: var(--shadow-glow);
}

.logo h1 {
    font-size: 1.75rem;
    font-weight: 700;
    background: var(--gradient-1);
    -webkit-background-clip: text;
    -webkit-text-fill-color: transparent;
    background-clip: text;
}

.header-stats {
    display: flex;
    gap: 20px;
}

.stat {
    text-align: center;
    padding: 8px 16px;
    background: var(--bg-secondary);
    border-radius: var(--radius-sm);
    border: 1px solid var(--border-color);
    min-width: 70px;
    transition: var(--transition);
}

.stat:hover {
    border-color: var(--accent);
    box-shadow: var(--shadow-glow);
}

.stat-value {
    display: block;
    font-size: 1.25rem;
    font-weight: 700;
    color: var(--accent);
}

.stat-label {
    display: block;
    font-size: 0.7rem;
    font-weight: 500;
    color: var(--text-secondary);
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

/* ===== Add Task Form ===== */
.add-task-section {
    margin-bottom: 24px;
}

.add-task-form {
    background: var(--bg-secondary);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-lg);
    padding: 20px;
    box-shadow: var(--shadow-md);
    transition: var(--transition);
}

.add-task-form:focus-within {
    border-color: var(--accent);
    box-shadow: var(--shadow-glow), var(--shadow-md);
}

.form-row {
    display: flex;
    gap: 12px;
    align-items: stretch;
}

.input-group {
    flex: 1;
}

.input-group-title {
    flex: 2;
}

.input-group input {
    width: 100%;
    padding: 12px 16px;
    background: var(--bg-input);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    color: var(--text-primary);
    font-family: inherit;
    font-size: 0.95rem;
    transition: var(--transition);
    outline: none;
}

.input-group input::placeholder {
    color: var(--text-secondary);
}

.input-group input:focus {
    border-color: var(--accent);
    box-shadow: 0 0 0 3px var(--accent-glow);
}

.btn {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    gap: 8px;
    padding: 12px 24px;
    border: none;
    border-radius: var(--radius-sm);
    font-family: inherit;
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    transition: var(--transition);
    white-space: nowrap;
}

.btn-add {
    background: var(--gradient-1);
    color: white;
    box-shadow: var(--shadow-sm);
}

.btn-add:hover {
    transform: translateY(-1px);
    box-shadow: var(--shadow-glow), var(--shadow-md);
}

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

/* ===== Filter Tabs ===== */
.filter-section {
    margin-bottom: 20px;
}

.filter-tabs {
    display: flex;
    background: var(--bg-secondary);
    border-radius: var(--radius-sm);
    padding: 4px;
    border: 1px solid var(--border-color);
    gap: 4px;
}

.filter-tab {
    flex: 1;
    padding: 10px 16px;
    background: transparent;
    border: none;
    border-radius: 6px;
    color: var(--text-secondary);
    font-family: inherit;
    font-size: 0.85rem;
    font-weight: 500;
    cursor: pointer;
    transition: var(--transition);
}

.filter-tab:hover {
    color: var(--text-primary);
    background: rgba(108, 99, 255, 0.08);
}

.filter-tab.active {
    background: var(--accent);
    color: white;
    box-shadow: var(--shadow-sm);
}

/* ===== Task List ===== */
.task-list {
    display: flex;
    flex-direction: column;
    gap: 12px;
}

.task-item {
    display: flex;
    align-items: center;
    gap: 16px;
    padding: 16px 20px;
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-md);
    transition: var(--transition);
    animation: slideIn 0.3s ease-out;
}

@keyframes slideIn {
    from {
        opacity: 0;
        transform: translateY(-10px);
    }
    to {
        opacity: 1;
        transform: translateY(0);
    }
}

.task-item:hover {
    background: var(--bg-card-hover);
    border-color: rgba(108, 99, 255, 0.3);
    box-shadow: var(--shadow-sm);
    transform: translateX(4px);
}

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

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

/* Checkbox */
.task-checkbox {
    position: relative;
    width: 24px;
    height: 24px;
    flex-shrink: 0;
}

.task-checkbox input {
    position: absolute;
    opacity: 0;
    width: 100%;
    height: 100%;
    cursor: pointer;
    z-index: 1;
}

.task-checkbox .checkmark {
    width: 24px;
    height: 24px;
    border: 2px solid var(--border-color);
    border-radius: 6px;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition);
}

.task-checkbox input:hover + .checkmark {
    border-color: var(--accent);
}

.task-checkbox input:checked + .checkmark {
    background: var(--success);
    border-color: var(--success);
}

.task-checkbox .checkmark svg {
    opacity: 0;
    transform: scale(0.5);
    transition: var(--transition);
    color: white;
}

.task-checkbox input:checked + .checkmark svg {
    opacity: 1;
    transform: scale(1);
}

/* Task Content */
.task-content {
    flex: 1;
    min-width: 0;
}

.task-title {
    font-size: 1rem;
    font-weight: 500;
    color: var(--text-primary);
    margin-bottom: 2px;
    word-break: break-word;
}

.task-description {
    font-size: 0.85rem;
    color: var(--text-secondary);
    word-break: break-word;
}

.task-meta {
    font-size: 0.7rem;
    color: var(--text-muted);
    margin-top: 4px;
}

/* Task Actions */
.task-actions {
    display: flex;
    gap: 8px;
    flex-shrink: 0;
    opacity: 0;
    transition: var(--transition);
}

.task-item:hover .task-actions {
    opacity: 1;
}

.btn-icon {
    width: 36px;
    height: 36px;
    border: none;
    border-radius: var(--radius-sm);
    background: transparent;
    color: var(--text-secondary);
    cursor: pointer;
    display: flex;
    align-items: center;
    justify-content: center;
    transition: var(--transition);
}

.btn-icon:hover {
    background: rgba(231, 76, 60, 0.15);
    color: var(--danger);
}

/* ===== Empty State ===== */
.empty-state {
    text-align: center;
    padding: 60px 20px;
    color: var(--text-secondary);
}

.empty-state svg {
    margin-bottom: 16px;
    opacity: 0.3;
}

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

/* ===== Loading State ===== */
.loading-state {
    text-align: center;
    padding: 60px 20px;
    color: var(--text-secondary);
}

.spinner {
    width: 40px;
    height: 40px;
    border: 3px solid var(--border-color);
    border-top-color: var(--accent);
    border-radius: 50%;
    margin: 0 auto 16px;
    animation: spin 0.8s linear infinite;
}

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

/* ===== Toast Notification ===== */
.toast {
    position: fixed;
    bottom: 24px;
    right: 24px;
    padding: 14px 24px;
    background: var(--bg-card);
    border: 1px solid var(--border-color);
    border-radius: var(--radius-sm);
    color: var(--text-primary);
    font-size: 0.9rem;
    font-weight: 500;
    box-shadow: var(--shadow-lg);
    transform: translateY(100px);
    opacity: 0;
    transition: all 0.35s cubic-bezier(0.4, 0, 0.2, 1);
    z-index: 1000;
    max-width: 360px;
}

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

.toast.success {
    border-left: 4px solid var(--success);
}

.toast.error {
    border-left: 4px solid var(--danger);
}

.toast.info {
    border-left: 4px solid var(--accent);
}

/* ===== Footer ===== */
.app-footer {
    margin-top: auto;
    padding: 24px 0;
    border-top: 1px solid var(--border-color);
    text-align: center;
}

.app-footer p {
    font-size: 0.8rem;
    color: var(--text-secondary);
}

/* ===== Responsive ===== */
@media (max-width: 640px) {
    .header-content {
        flex-direction: column;
        align-items: flex-start;
    }

    .header-stats {
        width: 100%;
        justify-content: space-between;
    }

    .stat {
        min-width: 0;
        flex: 1;
        padding: 6px 8px;
    }

    .form-row {
        flex-direction: column;
    }

    .btn-add {
        width: 100%;
        justify-content: center;
    }

    .task-actions {
        opacity: 1;
    }

    .logo h1 {
        font-size: 1.4rem;
    }
}