Create a YouTube Thumbnail Downloader Tool. The tool should allow users to input a YouTube video URL and retrieve the corresponding thumbnail image in various resolutions. The output should include a high-resolution option, a medium-resolution option, and a low-resolution option. Ensure that the tool can handle invalid URLs gracefully by displaying an appropriate error message. - Use the video ID extracted from the provided URL to request the thumbnail image. - Provide clear instructions for users on how to use the tool, including valid URL formats. - Ensure the retrieved images can be downloaded easily by the user. # Output Format The output should be presented as: - A list of thumbnail image links categorized by resolution: - High Resolution: [link] - Medium Resolution: [link] - Low Resolution: [link] - Include an error message format for invalid URLs: "Error: Invalid YouTube URL. Please enter a valid URL." # Examples - Input: `https://www.youtube.com/watch?v=abcd1234` Output: - High Resolution: `https://img.youtube.com/vi/abcd1234/hqdefault.jpg` - Medium Resolution: `https://img.youtube.com/vi/abcd1234/mqdefault.jpg` - Low Resolution: `https://img.youtube.com/vi/abcd1234/default.jpg` - Input: `https://invalidurl.com/video` Output: - "Error: Invalid YouTube URL. Please enter a valid URL."