:root {
    --primary-color: #38bdf8;
    --primary-dark: #0ea5e9;
    --success-color: #38bdf8;
    --danger-color: #ef4444;
    --bg-primary: #ffffff;
    --bg-secondary: #e0f2fe;
    --bg-tertiary: #bae6fd;
    --text-primary: #0f172a;
    --text-secondary: #334155;
    --border-color: #bae6fd;
    --shadow: 0 1px 3px rgba(15, 23, 42, 0.1);
    --shadow-lg: 0 10px 25px rgba(15, 23, 42, 0.12);
    
    /* Calendar colors - GitHub style */
    --level-0: #e2e8f0;
    --level-1: #bfdbfe;
    --level-2: #93c5fd;
    --level-3: #60a5fa;
    --level-4: #2563eb;
}

body.dark-mode {
    --primary-color: #3b82f6;
    --primary-dark: #2563eb;
    --success-color: #34d399;
    --danger-color: #f87171;
    --bg-primary: #1f2937;
    --bg-secondary: #111827;
    --bg-tertiary: #374151;
    --text-primary: #f9fafb;
    --text-secondary: #d1d5db;
    --border-color: #4b5563;
    --shadow: 0 1px 3px rgba(0, 0, 0, 0.3);
    --shadow-lg: 0 10px 25px rgba(0, 0, 0, 0.5);
    
    /* Dark mode calendar colors */
    --level-0: #374151;
    --level-1: #065f46;
    --level-2: #059669;
    --level-3: #10b981;
    --level-4: #34d399;
}

body.dark-mode {
    background: linear-gradient(135deg, #1e293b 0%, #0f172a 100%);
}

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

input,
button {
    font-family: inherit;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
    background: linear-gradient(135deg, #38bdf8 0%, #3b82f6 100%);
    min-height: 100vh;
    padding: 20px;
    color: var(--text-primary);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    -webkit-text-size-adjust: 100%;
    transition: background 0.3s ease;
}

.dark-mode-toggle {
    position: fixed;
    top: 20px;
    right: 20px;
    background: rgba(255, 255, 255, 0.2);
    border: 2px solid rgba(255, 255, 255, 0.3);
    border-radius: 50px;
    padding: 10px 20px;
    cursor: pointer;
    color: white;
    font-weight: 600;
    font-size: 1.1rem;
    backdrop-filter: blur(10px);
    transition: all 0.3s ease;
    z-index: 1000;
    display: flex;
    align-items: center;
    gap: 8px;
}

.dark-mode-toggle:hover {
    background: rgba(255, 255, 255, 0.3);
    transform: scale(1.05);
}

.dark-mode-toggle:active {
    transform: scale(0.95);
}

.container {
    max-width: 1200px;
    margin: 0 auto;
}

header {
    text-align: center;
    margin-bottom: 40px;
    color: white;
}

header h1 {
    font-size: 3rem;
    margin-bottom: 10px;
    text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.2);
}

.subtitle {
    font-size: 1.1rem;
    opacity: 0.95;
}

.add-habit-section {
    background: var(--bg-primary);
    padding: 30px;
    border-radius: 16px;
    box-shadow: var(--shadow-lg);
    margin-bottom: 30px;
    margin-top: 20px;
}

.habit-section-header {
    margin-bottom: 20px;
}

.habit-section-header h2 {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 5px;
}

.habit-subtitle {
    color: var(--text-secondary);
    font-size: 0.95rem;
}

.weekly-section {
    margin-bottom: 24px;
}

.weekly-card {
    background: var(--bg-primary);
    padding: 22px;
    border-radius: 16px;
    box-shadow: var(--shadow-lg);
    overflow-x: auto;
}

.weekly-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    gap: 12px;
    margin-bottom: 16px;
}

.weekly-header h2 {
    color: var(--text-primary);
    margin-bottom: 4px;
}

.weekly-subtitle {
    color: var(--text-secondary);
}

.weekly-range {
    font-weight: 700;
    color: var(--primary-color);
    background: var(--bg-secondary);
    padding: 10px 14px;
    border-radius: 12px;
    border: 1px solid var(--border-color);
}

.weekly-grid {
    display: flex;
    flex-direction: column;
    gap: 8px;
    min-height: 72px;
}

.weekly-row {
    display: grid;
    grid-template-columns: 1.4fr repeat(7, 1fr);
    gap: 8px;
    align-items: center;
    min-width: 760px;
}

.weekly-header-row {
    font-size: 0.85rem;
    color: var(--text-secondary);
    text-transform: uppercase;
    font-weight: 700;
}

.weekly-name-cell {
    background: var(--bg-secondary);
    padding: 12px 14px;
    border-radius: 10px;
    font-weight: 700;
    color: var(--text-primary);
    border: 1px solid var(--border-color);
}

.weekly-day-cell {
    background: var(--bg-secondary);
    padding: 10px 8px;
    border-radius: 10px;
    text-align: center;
    color: var(--text-primary);
    border: 1px solid var(--border-color);
    min-height: 62px;
    display: flex;
    flex-direction: column;
    justify-content: center;
    gap: 6px;
}

.weekly-day-cell.today {
    border: 2px solid var(--primary-color);
}

.weekly-day-cell.future {
    opacity: 0.6;
    cursor: not-allowed;
}

.week-day {
    font-weight: 700;
    color: var(--text-secondary);
}

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

.weekly-checkbox {
    display: flex;
    align-items: center;
    justify-content: center;
    cursor: pointer;
}

.weekly-checkbox input {
    display: none;
}

.weekly-checkbox span {
    width: 26px;
    height: 26px;
    border: 2px solid var(--border-color);
    border-radius: 8px;
    display: inline-block;
    background: var(--bg-tertiary);
    position: relative;
    transition: all 0.2s ease;
}

.weekly-checkbox input:checked + span {
    background: var(--success-color);
    border-color: var(--success-color);
    box-shadow: 0 4px 12px rgba(56, 189, 248, 0.35);
}

.weekly-checkbox span::after {
    content: '\2713';
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -55%);
    font-size: 16px;
    color: white;
    opacity: 0;
    transition: opacity 0.15s ease;
}

.weekly-checkbox input:checked + span::after {
    opacity: 1;
}

.weekly-empty {
    background: var(--bg-secondary);
    border: 1px dashed var(--border-color);
    padding: 16px;
    border-radius: 12px;
    color: var(--text-secondary);
    text-align: center;
}

.input-group {
    display: flex;
    gap: 12px;
}

#habitInput {
    flex: 1;
    padding: 14px 18px;
    border: 2px solid var(--border-color);
    border-radius: 10px;
    font-size: 1rem;
    transition: border-color 0.3s;
    font-family: inherit;
    -webkit-appearance: none;
    -moz-appearance: none;
    appearance: none;
}

#habitInput:focus {
    outline: none;
    border-color: var(--primary-color);
}

#addHabitBtn {
    padding: 14px 30px;
    background: var(--primary-color);
    color: white;
    border: none;
    border-radius: 10px;
    font-size: 1rem;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.3s, transform 0.1s;
    font-family: inherit;
    -webkit-appearance: none;
    -moz-appearance: none;
    appearance: none;
    -webkit-touch-callout: none;
}

#addHabitBtn:hover {
    background: var(--primary-dark);
}

#addHabitBtn:active {
    transform: scale(0.98);
}

.habits-container {
    display: flex;
    flex-direction: column;
    gap: 20px;
}

.habit-card {
    background: var(--bg-primary);
    padding: 25px;
    border-radius: 16px;
    box-shadow: var(--shadow-lg);
    animation: slideIn 0.3s ease-out;
}

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

.habit-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 20px;
    padding-bottom: 15px;
    border-bottom: 2px solid var(--bg-tertiary);
}

.habit-title {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-primary);
}

.habit-actions {
    display: flex;
    gap: 10px;
}

.mark-today-btn {
    padding: 8px 18px;
    background: var(--success-color);
    color: white;
    border: none;
    border-radius: 8px;
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    transition: all 0.3s;
}

.mark-today-btn:hover {
    background: var(--primary-dark);
    transform: translateY(-2px);
}

.mark-today-btn.completed {
    background: var(--text-secondary);
    cursor: default;
}

.mark-today-btn.completed:hover {
    transform: none;
}

.delete-habit-btn {
    padding: 8px 18px;
    background: var(--danger-color);
    color: white;
    border: none;
    border-radius: 8px;
    font-size: 0.9rem;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.3s;
}

.delete-habit-btn:hover {
    background: #dc2626;
}

.stats-row {
    display: flex;
    gap: 20px;
    margin-bottom: 20px;
    flex-wrap: wrap;
}

.stat-box {
    flex: 1;
    min-width: 150px;
    background: var(--bg-secondary);
    padding: 15px;
    border-radius: 10px;
    text-align: center;
}

.stat-label {
    font-size: 0.85rem;
    color: var(--text-secondary);
    margin-bottom: 5px;
    text-transform: uppercase;
    letter-spacing: 0.5px;
}

.stat-value {
    font-size: 1.8rem;
    font-weight: 700;
    color: var(--primary-color);
}

.calendar-section {
    margin-top: 20px;
}

.calendar-header {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: 15px;
}

.calendar-title {
    font-size: 1rem;
    font-weight: 600;
    color: var(--text-secondary);
}

.calendar-grid {
    display: grid;
    grid-template-columns: repeat(auto-fill, minmax(28px, 1fr));
    gap: 4px;
    margin-bottom: 10px;
}

.day-cell {
    aspect-ratio: 1;
    background: var(--level-0);
    border-radius: 4px;
    cursor: pointer;
    transition: all 0.2s;
    position: relative;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 0.7rem;
    color: var(--text-secondary);
}

.day-cell:hover {
    transform: scale(1.1);
    box-shadow: 0 2px 8px rgba(0, 0, 0, 0.15);
    z-index: 10;
}

.day-cell.completed {
    background: var(--level-4);
    color: white;
}

.day-cell.today {
    border: 2px solid var(--primary-color);
}

.day-cell.future {
    background: var(--bg-tertiary);
    opacity: 0.5;
    cursor: not-allowed;
}

.day-cell .tooltip {
    position: absolute;
    bottom: 100%;
    left: 50%;
    transform: translateX(-50%);
    background: rgba(0, 0, 0, 0.9);
    color: white;
    padding: 6px 10px;
    border-radius: 6px;
    font-size: 0.75rem;
    white-space: nowrap;
    pointer-events: none;
    opacity: 0;
    transition: opacity 0.2s;
    margin-bottom: 5px;
    z-index: 100;
}

.day-cell:hover .tooltip {
    opacity: 1;
}

.calendar-legend {
    display: flex;
    align-items: center;
    gap: 8px;
    font-size: 0.85rem;
    color: var(--text-secondary);
    margin-top: 15px;
}

.legend-item {
    display: flex;
    align-items: center;
    gap: 5px;
}

.legend-box {
    width: 16px;
    height: 16px;
    border-radius: 3px;
}

.empty-state {
    display: none;
    text-align: center;
    background: var(--bg-primary);
    padding: 60px 40px;
    border-radius: 16px;
    box-shadow: var(--shadow-lg);
}

.empty-state.show {
    display: block;
}

.empty-icon {
    font-size: 4rem;
    margin-bottom: 20px;
}

.empty-state h3 {
    font-size: 1.5rem;
    margin-bottom: 10px;
    color: var(--text-primary);
}

.empty-state p {
    color: var(--text-secondary);
    font-size: 1.1rem;
}

/* Todo List Styles */
.todo-section {
    margin-top: 30px;
    margin-bottom: 40px;
}

.todo-card {
    background: var(--bg-primary);
    padding: 25px;
    border-radius: 16px;
    box-shadow: var(--shadow-lg);
    animation: slideIn 0.3s ease-out;
}

.todo-header {
    margin-bottom: 20px;
}

.todo-header h2 {
    font-size: 1.5rem;
    font-weight: 700;
    color: var(--text-primary);
    margin-bottom: 5px;
}

.todo-subtitle {
    color: var(--text-secondary);
    font-size: 0.95rem;
}

.todo-input-group {
    display: flex;
    gap: 12px;
    margin-bottom: 20px;
}

#todoInput {
    flex: 1;
    padding: 12px 16px;
    border: 2px solid var(--border-color);
    border-radius: 10px;
    font-size: 0.95rem;
    transition: border-color 0.3s;
    font-family: inherit;
    -webkit-appearance: none;
    -moz-appearance: none;
    appearance: none;
}

#todoInput:focus {
    outline: none;
    border-color: var(--primary-color);
}

#addTodoBtn {
    padding: 12px 24px;
    background: var(--primary-color);
    color: white;
    border: none;
    border-radius: 10px;
    font-size: 0.95rem;
    font-weight: 600;
    cursor: pointer;
    transition: background 0.3s, transform 0.1s;
    font-family: inherit;
    -webkit-appearance: none;
    -moz-appearance: none;
    appearance: none;
    -webkit-touch-callout: none;
}

#addTodoBtn:hover {
    background: var(--primary-dark);
}

#addTodoBtn:active {
    transform: scale(0.98);
}

.todo-list {
    display: flex;
    flex-direction: column;
    gap: 10px;
    max-height: 400px;
    overflow-y: auto;
}

.todo-list::-webkit-scrollbar {
    width: 6px;
}

.todo-list::-webkit-scrollbar-track {
    background: transparent;
}

.todo-list::-webkit-scrollbar-thumb {
    background: var(--border-color);
    border-radius: 3px;
}

.todo-list::-webkit-scrollbar-thumb:hover {
    background: var(--text-secondary);
}

.todo-item {
    display: flex;
    align-items: center;
    gap: 12px;
    padding: 12px 14px;
    background: var(--bg-secondary);
    border-radius: 10px;
    border: 1px solid var(--border-color);
    transition: all 0.2s;
    animation: slideIn 0.2s ease-out;
}

.todo-item:hover {
    background: var(--bg-tertiary);
    border-color: var(--primary-color);
}

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

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

.todo-checkbox {
    position: relative;
    display: flex;
    align-items: center;
}

.todo-checkbox input {
    display: none;
}

.todo-checkbox label {
    display: flex;
    align-items: center;
    cursor: pointer;
}

.checkmark {
    display: inline-flex;
    align-items: center;
    justify-content: center;
    width: 24px;
    height: 24px;
    border: 2px solid var(--border-color);
    border-radius: 6px;
    background: transparent;
    transition: all 0.2s;
    flex-shrink: 0;
}

.todo-checkbox input:checked + label .checkmark {
    background: var(--success-color);
    border-color: var(--success-color);
    box-shadow: 0 4px 12px rgba(56, 189, 248, 0.25);
}

.todo-checkbox input:checked + label .checkmark::after {
    content: '✓';
    color: white;
    font-size: 14px;
    font-weight: bold;
}

.todo-text {
    flex: 1;
    color: var(--text-primary);
    word-break: break-word;
}

.todo-delete-btn {
    padding: 4px 8px;
    background: transparent;
    color: var(--danger-color);
    border: none;
    border-radius: 6px;
    font-size: 1.4rem;
    cursor: pointer;
    transition: all 0.2s;
    line-height: 1;
    flex-shrink: 0;
}

.todo-delete-btn:hover {
    background: rgba(239, 68, 68, 0.1);
    color: #dc2626;
}

.todo-empty {
    display: none;
    text-align: center;
    padding: 30px 20px;
    color: var(--text-secondary);
}

.todo-empty.show {
    display: block;
}

.todo-empty p {
    margin: 0;
    font-size: 0.95rem;
}

@media (max-width: 768px) {
    header h1 {
        font-size: 2rem;
    }
    
    .input-group {
        flex-direction: column;
    }

    .todo-input-group {
        flex-direction: column;
    }
    
    .habit-header {
        flex-direction: column;
        align-items: flex-start;
        gap: 15px;
    }
    
    .stats-row {
        flex-direction: column;
    }
    
    .calendar-grid {
        grid-template-columns: repeat(7, 1fr);
    }

    .todo-list {
        max-height: 300px;
    }
}