Javascript Draw on Canvas with Mouse

<div class="container">
  <h1>Canvas Drawing App</h1>

  <div class="toolbar">
    <div class="tool-group">
      <label>Color:</label>
      <input type="color" id="colorPicker" class="color-picker" value="#000000">
    </div>

    <div class="divider"></div>

    <div class="tool-group">
      <label>Size:</label>
      <input type="range" id="sizeSlider" class="size-slider" min="1" max="50" value="5">
      <span class="size-value" id="sizeValue">5px</span>
    </div>

    <div class="divider"></div>

    <button class="btn btn-secondary" id="clearBtn">Clear Canvas</button>
    <button class="btn btn-primary" id="downloadBtn">Download</button>
  </div>

  <div class="canvas-wrapper">
    <canvas id="drawingCanvas" width="850" height="500"></canvas>
  </div>
</div> 

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

        body {
            font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, sans-serif;
            background: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
            min-height: 100vh;
            display: flex;
            align-items: center;
            justify-content: center;
            padding: 20px;
        }

        .container {
            background: white;
            border-radius: 12px;
            padding: 24px;
            box-shadow: 0 20px 60px rgba(0, 0, 0, 0.3);
            max-width: 900px;
            width: 100%;
        }

        h1 {
            font-size: 24px;
            color: #2d3748;
            margin-bottom: 20px;
            text-align: center;
        }

        .toolbar {
            display: flex;
            gap: 12px;
            margin-bottom: 20px;
            flex-wrap: wrap;
            align-items: center;
            padding: 16px;
            background: #f7fafc;
            border-radius: 8px;
        }

        .tool-group {
            display: flex;
            align-items: center;
            gap: 8px;
        }

        .tool-group label {
            font-size: 14px;
            color: #4a5568;
            font-weight: 600;
        }

        .color-picker {
            width: 50px;
            height: 40px;
            border: 2px solid #e2e8f0;
            border-radius: 6px;
            cursor: pointer;
            transition: all 0.2s;
        }

        .color-picker:hover {
            border-color: #4facfe;
            transform: scale(1.05);
        }

        .size-slider {
            width: 120px;
            height: 6px;
            border-radius: 3px;
            background: #e2e8f0;
            outline: none;
            cursor: pointer;
        }

        .size-slider::-webkit-slider-thumb {
            appearance: none;
            width: 18px;
            height: 18px;
            border-radius: 50%;
            background: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
            cursor: pointer;
            transition: all 0.2s;
        }

        .size-slider::-webkit-slider-thumb:hover {
            transform: scale(1.2);
        }

        .size-value {
            font-size: 14px;
            color: #2d3748;
            font-weight: 600;
            min-width: 30px;
        }

        .btn {
            padding: 10px 18px;
            border: none;
            border-radius: 6px;
            font-size: 14px;
            font-weight: 600;
            cursor: pointer;
            transition: all 0.2s;
        }

        .btn-primary {
            background: linear-gradient(135deg, #4facfe 0%, #00f2fe 100%);
            color: white;
        }

        .btn-primary:hover {
            transform: translateY(-2px);
            box-shadow: 0 4px 12px rgba(79, 172, 254, 0.4);
        }

        .btn-secondary {
            background: #e2e8f0;
            color: #4a5568;
        }

        .btn-secondary:hover {
            background: #cbd5e0;
        }

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

        .canvas-wrapper {
            border: 3px solid #e2e8f0;
            border-radius: 8px;
            overflow: hidden;
            box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
            background: white;
            cursor: crosshair;
        }

        canvas {
            display: block;
            touch-action: none;
        }

        .divider {
            width: 1px;
            height: 30px;
            background: #cbd5e0;
            margin: 0 4px;
        }

   const canvas = document.getElementById('drawingCanvas');
        const ctx = canvas.getContext('2d');
        const colorPicker = document.getElementById('colorPicker');
        const sizeSlider = document.getElementById('sizeSlider');
        const sizeValue = document.getElementById('sizeValue');
        const clearBtn = document.getElementById('clearBtn');
        const downloadBtn = document.getElementById('downloadBtn');

        let isDrawing = false;
        let lastX = 0;
        let lastY = 0;

        // Initialize canvas with white background
        ctx.fillStyle = 'white';
        ctx.fillRect(0, 0, canvas.width, canvas.height);
        
        // Set default drawing style
        ctx.lineCap = 'round';
        ctx.lineJoin = 'round';

        function startDrawing(e) {
            isDrawing = true;
            const rect = canvas.getBoundingClientRect();
            lastX = e.clientX - rect.left;
            lastY = e.clientY - rect.top;
        }

        function draw(e) {
            if (!isDrawing) return;

            const rect = canvas.getBoundingClientRect();
            const currentX = e.clientX - rect.left;
            const currentY = e.clientY - rect.top;

            ctx.strokeStyle = colorPicker.value;
            ctx.lineWidth = sizeSlider.value;

            ctx.beginPath();
            ctx.moveTo(lastX, lastY);
            ctx.lineTo(currentX, currentY);
            ctx.stroke();

            lastX = currentX;
            lastY = currentY;
        }

        function stopDrawing() {
            isDrawing = false;
        }

        function clearCanvas() {
            ctx.fillStyle = 'white';
            ctx.fillRect(0, 0, canvas.width, canvas.height);
        }

        function downloadCanvas() {
            const link = document.createElement('a');
            link.download = 'drawing.png';
            link.href = canvas.toDataURL();
            link.click();
        }

        // Mouse events
        canvas.addEventListener('mousedown', startDrawing);
        canvas.addEventListener('mousemove', draw);
        canvas.addEventListener('mouseup', stopDrawing);
        canvas.addEventListener('mouseout', stopDrawing);

        // Touch events for mobile
        canvas.addEventListener('touchstart', (e) => {
            e.preventDefault();
            const touch = e.touches[0];
            const mouseEvent = new MouseEvent('mousedown', {
                clientX: touch.clientX,
                clientY: touch.clientY
            });
            canvas.dispatchEvent(mouseEvent);
        });

        canvas.addEventListener('touchmove', (e) => {
            e.preventDefault();
            const touch = e.touches[0];
            const mouseEvent = new MouseEvent('mousemove', {
                clientX: touch.clientX,
                clientY: touch.clientY
            });
            canvas.dispatchEvent(mouseEvent);
        });

        canvas.addEventListener('touchend', (e) => {
            e.preventDefault();
            const mouseEvent = new MouseEvent('mouseup', {});
            canvas.dispatchEvent(mouseEvent);
        });

        // Update size value display
        sizeSlider.addEventListener('input', () => {
            sizeValue.textContent = `${sizeSlider.value}px`;
        });

        // Button events
        clearBtn.addEventListener('click', clearCanvas);
        downloadBtn.addEventListener('click', downloadCanvas);