Creating a complete online photo editor with HTML, CSS, and JavaScript is a complex task that goes beyond the scope of a single response. However, I can provide you with a simplified example of an online photo editor with basic functionality, responsive design, and some colorful styling. For a production-ready online photo editor, you would typically need to use a graphics library like Fabric.js or Konva.js to handle image manipulation. Please note that for such a project, you may also need server-side code to handle file uploads and processing. Here's a basic example: ```html

Online Photo Editor

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This example provides basic image loading, rotation, and flipping functionality. For a more comprehensive online photo editor, you would need to integrate a graphics library like Fabric.js or Konva.js and implement more advanced features like cropping, resizing, and filters. Additionally, you would need server-side code to handle image uploads and processing.