Step 1: Check if the code has any syntax errors.

Here is the code to check:
<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Enhanced To-Do List with Calendar</title>
    <style>
        /* Reset some default styles */
        * {
            box-sizing: border-box;
            margin: 0;
            padding: 0;
        }

        body {
            background: linear-gradient(135deg, #ece9e6, #ffffff);
            font-family: 'Roboto', sans-serif;
            display: flex;
            justify-content: center;
            align-items: flex-start;
            min-height: 100vh;
            padding: 30px 20px;
        }

        .container {
            background: #ffffff;
            border-radius: 16px;
            box-shadow: 0 20px 40px rgba(0, 0, 0, 0.1);
            width: 100%;
            max-width: 1000px;
            padding: 40px 30px;
            display: flex;
            flex-wrap: wrap;
            gap: 30px;
            animation: slideIn 0.5s ease-out;
        }

        @keyframes slideIn {
            from {
                opacity: 0;
                transform: translateY(-50px);
            }
            to {
                opacity: 1;
                transform: translateY(0);
            }
        }

        h1, h2 {
            color: #333;
        }

        h1 {
            text-align: center;
            width: 100%;
            margin-bottom: 30px;
            font-size: 2.5em;
            letter-spacing: 1px;
        }

        /* To-Do List Styles */
        .todo-section {
            flex: 1 1 400px;
        }

        .input-group {
            display: flex;
            margin-bottom: 25px;
        }

        #new-task {
            flex: 1;
            padding: 12px 18px;
            border: 2px solid #ddd;
            border-right: none;
            border-radius: 8px 0 0 8px;
            font-size: 16px;
            transition: border-color 0.3s, box-shadow 0.3s;
        }

        #new-task:focus {
            outline: none;
            border-color: #6200ea;
            box-shadow: 0 0 5px rgba(98, 0, 234, 0.5);
        }

        #add-task {
            padding: 12px 20px;
            border: none;
            background-color: #6200ea;
            color: #fff;
            font-size: 16px;
            border-radius: 0 8px 8px 0;
            cursor: pointer;
            transition: background-color 0.3s, transform 0.2s;
        }

        #add-task:hover {
            background-color: #3700b3;
            transform: translateY(-2px);
        }

        #add-task:active {
            transform: translateY(0);
        }

        .filters {
            display: flex;
            justify-content: center;
            margin-bottom: 20px;
        }

        .filter-btn {
            background: none;
            border: none;
            margin: 0 10px;
            font-size: 16px;
            cursor: pointer;
            color: #777;
            position: relative;
            transition: color 0.3s;
        }

        .filter-btn.active, .filter-btn:hover {
            color: #6200ea;
        }

        .filter-btn.active::after {
            content: '';
            position: absolute;
            bottom: -5px;
            left: 50%;
            transform: translateX(-50%);
            width: 50%;
            height: 3px;
            background-color: #6200ea;
            border-radius: 2px;
        }

        ul {
            list-style: none;
        }

        li {
            background: #f9f9f9;
            padding: 15px 20px;
            margin-bottom: 12px;
            border-radius: 8px;
            display: flex;
            justify-content: space-between;
            align-items: center;
            opacity: 1;
            transform: translateY(0);
            transition: all 0.3s ease;
            cursor: grab;
            position: relative;
        }

        li.dragging {
            opacity: 0.5;
            transform: scale(1.05);
            cursor: grabbing;
        }

        li.completed .task {
            text-decoration: line-through;
            color: #999;
        }

        li.hidden {
            opacity: 0;
            transform: translateX(100%);
            height: 0;
            margin: 0;
            padding: 0;
            overflow: hidden;
        }

        .task {
            flex: 1;
            cursor: pointer;
            transition: color 0.3s, text-decoration 0.3s;
            position: relative;
            padding-right: 30px; /* Space for delete button */
        }

        .task.editing {
            border-bottom: 1px dashed #6200ea;
        }

        .task-input {
            width: 100%;
            padding: 8px;
            font-size: 16px;
            border: 1px solid #6200ea;
            border-radius: 4px;
            outline: none;
        }

        .delete-btn {
            background: none;
            border: none;
            color: #e53935;
            font-size: 20px;
            cursor: pointer;
            transition: color 0.3s;
            margin-left: 15px;
            position: absolute;
            right: 10px;
            top: 50%;
            transform: translateY(-50%);
        }

        .delete-btn:hover {
            color: #b71c1c;
        }

        /* Add smooth appearance for new tasks */
        li.new-task {
            opacity: 0;
            transform: translateY(-20px);
            animation: fadeIn 0.5s forwards;
        }

        @keyframes fadeIn {
            to {
                opacity: 1;
                transform: translateY(0);
            }
        }

        /* Calendar Styles */
        .calendar-section {
            flex: 1 1 400px;
        }

        .calendar {
            width: 100%;
            max-width: 400px;
            margin: 0 auto;
            border: 1px solid #ddd;
            border-radius: 8px;
            overflow: hidden;
            box-shadow: 0 10px 20px rgba(0,0,0,0.1);
            transition: transform 0.3s;
        }

        .calendar-header {
            background-color: #6200ea;
            color: #fff;
            padding: 15px;
            text-align: center;
            position: relative;
        }

        .calendar-header h2 {
            margin-bottom: 10px;
            font-size: 1.5em;
        }

        .calendar-header .nav-btn {
            position: absolute;
            top: 50%;
            transform: translateY(-50%);
            background: none;
            border: none;
            color: #fff;
            font-size: 1.2em;
            cursor: pointer;
            padding: 5px 10px;
            transition: background-color 0.3s;
        }

        .calendar-header .nav-btn:hover {
            background-color: rgba(255, 255, 255, 0.2);
            border-radius: 4px;
        }

        .calendar-body {
            padding: 10px;
        }

        .calendar-weekdays, .calendar-dates {
            display: grid;
            grid-template-columns: repeat(7, 1fr);
            text-align: center;
            margin-bottom: 10px;
        }

        .calendar-weekdays div {
            font-weight: bold;
            padding: 8px 0;
            color: #555;
            background-color: #f0f0f0;
            border-radius: 4px;
        }

        .calendar-dates div {
            padding: 10px 0;
            margin-bottom: 5px;
            cursor: pointer;
            border-radius: 4px;
            transition: background-color 0.3s, color 0.3s;
            position: relative;
            min-height: 50px; /* Ensure consistent height */
            display: flex;
            flex-direction: column;
            align-items: center;
            justify-content: center;
        }

        .calendar-dates div:hover {
            background-color: #f0f0f0;
        }

        .calendar-dates .selected {
            background-color: #6200ea;
            color: #fff;
        }

        .calendar-dates .has-tasks::after {
            content: '';
            width: 6px;
            height: 6px;
            background-color: #e53935;
            border-radius: 50%;
            position: absolute;
            bottom: 5px;
            right: 5px;
        }

        /* Task Counts on Calendar */
        .calendar-dates .task-count::after {
            content: attr(data-count) " task(s)";
            position: absolute;
            bottom: -20px;
            left: 50%;
            transform: translateX(-50%);
            background-color: #6200ea;
            color: #fff;
            padding: 2px 6px;
            border-radius: 12px;
            font-size: 0.8em;
            opacity: 0;
            transition: opacity 0.3s;
            white-space: nowrap;
        }

        .calendar-dates div:hover .task-count::after {
            opacity: 1;
        }

        /* Responsive Design */
        @media (max-width: 800px) {
            .container {
                flex-direction: column;
                align-items: center;
            }

            .todo-section, .calendar-section {
                max-width: 100%;
            }

            .calendar {
                max-width: 100%;
            }
        }

        @media (max-width: 500px) {
            .calendar-weekdays div, .calendar-dates div {
                padding: 8px 0;
                font-size: 0.9em;
                min-height: 40px;
            }

            .task-count::after {
                font-size: 0.7em;
            }

            .filter-btn {
                margin: 0 5px;
                font-size: 14px;
            }

            #add-task, #new-task {
                font-size: 14px;
            }

            #add-task {
                padding: 10px 16px;
            }

            #new-task {
                padding: 10px 14px;
            }

            .delete-btn {
                font-size: 18px;
                margin-left: 10px;
            }
        }
    </style>
</head>
<body>

    <div class="container">
        <div class="todo-section">
            <h1>To-Do List</h1>
            <div class="input-group">
                <input type="text" id="new-task" placeholder="Add a new task...">
                <button id="add-task">Add</button>
            </div>
            <div class="filters">
                <button class="filter-btn active" data-filter="all">All</button>
                <button class="filter-btn" data-filter="active">Active</button>
                <button class="filter-btn" data-filter="completed">Completed</button>
            </div>
            <ul id="task-list">
                <!-- Tasks will appear here -->
            </ul>
        </div>

        <div class="calendar-section">
            <div class="calendar">
                <div class="calendar-header">
                    <button class="nav-btn" id="prev-month">&#9664;</button>
                    <h2 id="month-year">September 2024</h2>
                    <button class="nav-btn" id="next-month">&#9654;</button>
                </div>
                <div class="calendar-body">
                    <div class="calendar-weekdays">
                        <div>Sun</div>
                        <div>Mon</div>
                        <div>Tue</div>
                        <div>Wed</div>
                        <div>Thu</div>
                        <div>Fri</div>
                        <div>Sat</div>
                    </div>
                    <div class="calendar-dates" id="calendar-dates">
                        <!-- Dates will be generated here -->
                    </div>
                </div>
            </div>
        </div>
    </div>

    <script>
        document.addEventListener('DOMContentLoaded', () => {
            // To-Do List Functionality
            const addTaskButton = document.getElementById('add-task');
            const taskInput = document.getElementById('new-task');
            const taskList = document.getElementById('task-list');
            const filterButtons = document.querySelectorAll('.filter-btn');
            let currentFilter = 'all';
            let selectedDate = null; // To track selected date on calendar

            // Load tasks from localStorage
            let tasks = JSON.parse(localStorage.getItem('tasks')) || [];

            // Function to save tasks to localStorage
            function saveTasks() {
                localStorage.setItem('tasks', JSON.stringify(tasks));
            }

            // Function to render tasks based on filter and selected date
            function renderTasks() {
                taskList.innerHTML = '';
                let filteredTasks = tasks;

                if (currentFilter === 'active') {
                    filteredTasks = tasks.filter(task => !task.completed);
                } else if (currentFilter === 'completed') {
                    filteredTasks = tasks.filter(task => task.completed);
                }

                if (selectedDate) {
                    const dateStr = selectedDate.toISOString().split('T')[0];
                    filteredTasks = filteredTasks.filter(task => task.date === dateStr);
                }

                filteredTasks.forEach((task, index) => {
                    const li = createTaskElement(task.text, task.completed, index);
                    taskList.appendChild(li);
                });
            }

            // Function to create a new task element
            function createTaskElement(taskText, completed = false, index = 0) {
                const li = document.createElement('li');
                li.draggable = true;
                li.dataset.index = index;

                if (completed) {
                    li.classList.add('completed');
                }

                const span = document.createElement('span');
                span.classList.add('task');
                span.textContent = taskText;

                const deleteBtn = document.createElement('button');
                deleteBtn.classList.add('delete-btn');
                deleteBtn.innerHTML = '&times;';

                li.appendChild(span);
                li.appendChild(deleteBtn);

                // Add event listeners for drag and drop
                li.addEventListener('dragstart', handleDragStart);
                li.addEventListener('dragover', handleDragOver);
                li.addEventListener('drop', handleDrop);
                li.addEventListener('dragend', handleDragEnd);

                return li;
            }

            // Function to add a new task
            function addTask() {
                const taskText = taskInput.value.trim();
                if (taskText === '') return;

                const newTask = {
                    text: taskText,
                    completed: false,
                    date: selectedDate ? selectedDate.toISOString().split('T')[0] : null
                };
                tasks.unshift(newTask);
                saveTasks();
                renderTasks();
                updateCalendar();

                // Clear input
                taskInput.value = '';
                taskInput.focus();
            }

            // Event listener for adding task via button
            addTaskButton.addEventListener('click', addTask);

            // Event listener for adding task via Enter key
            taskInput.addEventListener('keypress', (e) => {
                if (e.key === 'Enter') {
                    addTask();
                }
            });

            // Event delegation for task interactions
            taskList.addEventListener('click', (e) => {
                const target = e.target;
                const li = target.closest('li');
                if (!li) return;
                const index = li.dataset.index;

                // Delete task
                if (target.classList.contains('delete-btn')) {
                    li.classList.add('hidden');
                    li.addEventListener('transitionend', () => {
                        tasks.splice(index, 1);
                        saveTasks();
                        renderTasks();
                        updateCalendar();
                    });
                }

                // Toggle complete
                if (target.classList.contains('task')) {
                    tasks[index].completed = !tasks[index].completed;
                    saveTasks();
                    renderTasks();
                    updateCalendar();
                }
            });

            // Event delegation for editing tasks
            taskList.addEventListener('dblclick', (e) => {
                const target = e.target;
                if (target.classList.contains('task')) {
                    const li = target.parentElement;
                    const index = li.dataset.index;
                    const currentText = tasks[index].text;

                    // Create input field
                    const input = document.createElement('input');
                    input.type = 'text';
                    input.classList.add('task-input');
                    input.value = currentText;
                    li.replaceChild(input, target);
                    input.focus();
                    input.select();

                    // Handle input events
                    input.addEventListener('keypress', (e) => {
                        if (e.key === 'Enter') {
                            const newText = input.value.trim();
                            if (newText !== '') {
                                tasks[index].text = newText;
                                saveTasks();
                                renderTasks();
                                updateCalendar();
                            }
                        }
                    });

                    input.addEventListener('blur', () => {
                        renderTasks();
                    });
                }
            });

            // Filter functionality
            filterButtons.forEach(button => {
                button.addEventListener('click', () => {
                    filterButtons.forEach(btn => btn.classList.remove('active'));
                    button.classList.add('active');
                    currentFilter = button.dataset.filter;
                    renderTasks();
                });
            });

            // Drag and Drop Handlers
            let dragSrcEl = null;

            function handleDragStart(e) {
                dragSrcEl = this;
                e.dataTransfer.effectAllowed = 'move';
                e.dataTransfer.setData('text/html', this.innerHTML);
                this.classList.add('dragging');
            }

            function handleDragOver(e) {
                if (e.preventDefault) {
                    e.preventDefault();
                }
                e.dataTransfer.dropEffect = 'move';
                return false;
            }

            function handleDrop(e) {
                if (e.stopPropagation) {
                    e.stopPropagation();
                }
                if (dragSrcEl !== this) {
                    const srcIndex = dragSrcEl.dataset.index;
                    const targetIndex = this.dataset.index;

                    // Swap tasks
                    [tasks[srcIndex], tasks[targetIndex]] = [tasks[targetIndex], tasks[srcIndex]];
                    saveTasks();
                    renderTasks();
                    updateCalendar();
                }
                return false;
            }

            function handleDragEnd() {
                this.classList.remove('dragging');
            }

            // Calendar Functionality
            const calendarDates = document.getElementById('calendar-dates');
            const monthYear = document.getElementById('month-year');
            const prevMonthBtn = document.getElementById('prev-month');
            const nextMonthBtn = document.getElementById('next-month');
            const calendarWeekdays = ['Sun', 'Mon', 'Tue', 'Wed', 'Thu', 'Fri', 'Sat'];

            let currentDate = new Date();

            // Function to render the calendar
            function renderCalendar() {
                calendarDates.innerHTML = '';
                const year = currentDate.getFullYear();
                const month = currentDate.getMonth();

                // Update month-year display
                const options = { month: 'long', year: 'numeric' };
                monthYear.textContent = currentDate.toLocaleDateString(undefined, options);

                // Get first day of the month
                const firstDay = new Date(year, month, 1).getDay();
                // Get number of days in the month
                const daysInMonth = new Date(year, month + 1, 0).getDate();

                // Fill in blank days
                for (let i = 0; i < firstDay; i++) {
                    const blankDiv = document.createElement('div');
                    calendarDates.appendChild(blankDiv);
                }

                // Fill in the days
                for (let day = 1; day <= daysInMonth; day++) {
                    const dateDiv = document.createElement('div');
                    dateDiv.textContent = day;
                    const dateObj = new Date(year, month, day);
                    const dateStr = dateObj.toISOString().split('T')[0];

                    // Check if there are tasks for this date
                    const tasksForDate = tasks.filter(task => task.date === dateStr);
                    if (tasksForDate.length > 0) {
                        dateDiv.classList.add('has-tasks');
                        const countSpan = document.createElement('span');
                        countSpan.classList.add('task-count');
                        countSpan.setAttribute('data-count', tasksForDate.length);
                        dateDiv.appendChild(countSpan);
                    }

                    // Highlight selected date
                    if (selectedDate && dateStr === selectedDate.toISOString().split('T')[0]) {
                        dateDiv.classList.add('selected');
                    }

                    // Add click event to select date
                    dateDiv.addEventListener('click', () => {
                        if (selectedDate && dateStr === selectedDate.toISOString().split('T')[0]) {
                            // Deselect if already selected
                            selectedDate = null;
                        } else {
                            selectedDate = new Date(year, month, day);
                        }
                        renderCalendar();
                        renderTasks();
                    });

                    calendarDates.appendChild(dateDiv);
                }
            }

            // Function to update calendar task indicators
            function updateCalendar() {
                renderCalendar();
            }

            // Event listeners for month navigation
            prevMonthBtn.addEventListener('click', () => {
                currentDate.setMonth(currentDate.getMonth() - 1);
                renderCalendar();
            });

            nextMonthBtn.addEventListener('click', () => {
                currentDate.setMonth(currentDate.getMonth() + 1);
                renderCalendar();
            });

            // Initial render
            renderCalendar();
            renderTasks();
        });
    </script>

</body>
</html>


Provide a detailed response indicating whether the code passes this check. If it does not, explain the issues.