For a more flexible tool that lets you tweak ChatGPT parameters and styling, I suggest MindMac, a native macOS app that offers a lot of control, including full OpenAI parameter control, styling, and support for multiple languages. It also has keyboard shortcuts, secure API key storage and a context mode for greater productivity. It costs $29 for basic use, but it's worth it for many people.
Another good option is StylerGPT, a browser extension that lets you customize ChatGPT's styling with 25 color schemes, 100 high-resolution backgrounds and the ability to upload your own images. It works with Chrome and Edge, among other browsers, and supports several ChatGPT models, including GPT-4. It's free, so it's a good way to make ChatGPT look more appealing without paying extra.
If you want to build ChatGPT into your website, Chattie is a no-code service that lets you embed ChatGPT and customize its styling with a built-in theme editor that supports full CSS styling. The service also offers automated prompt generation and analytics, so it's good for boosting user engagement and interaction on your website. It offers several pricing tiers, including a free trial.