Add simple docs page on custom CSS in DHC

Author: olayway

datahub-cloud/Customize Your DataHub Cloud Site with CSS.md

@@ -0,0 +1,22 @@
+---
+title: Customize Your Site with CSS
+---
+
+You can customize the appearance of your DataHub Cloud site by adding a `custom.css` file to your site's repository.
+
+## File Location
+
+Place the `custom.css` file in:
+- The root directory of your repository, or
+- The directory specified in your site's "Root Directory" setting (if you're publishing from a subfolder)
+
+## Creating the File
+
+1. Create a new file named `custom.css` in the appropriate location
+2. Add your CSS rules to customize colors, fonts, layouts, and more
+3. Commit and sync your site to apply the changes
+
+> [!important]
+> When using h1 tags in custom components, you must set `display: block !important;` in your CSS due to how page titles are handled internally.
+
+For a detailed guide on styling your site, including examples and step-by-step instructions, check out our [CSS styling tutorial](https://datahub.io/blog/style-your-datahub-cloud-site-with-css).