Launch Week Day 3: Global CSS

With the addition of Global CSS, users can now fully customize their documentation design, including setting global CSS for specific tags and creating reusable CSS classes. This feature is available on the business plan and enables fine-tuning of colors, formatting, and more. The goal of this feature is to make Mintlify docs adaptable and opinionated, allowing users to tailor the design to fit seamlessly into their brand and online presence. To get started, users can upgrade their CLI with `npm i -g mintlify@latest` and add a CSS file to their docs repository. Global CSS will be launched in beta with the Pro Plan, providing users with more control over their documentation design.