doc: save refactor/WP-791-dropdown-menu PR desc

refactor-WP-791-dropdown-menu-pr-desc.md

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+## Overview
+
+Refactor the styles for Data Files dropdown menus to:
+- share more CSS
+- use clearer CSS
+
+## Related
+
+* [WP-791](https://tacc-main.atlassian.net/browse/WP-791)
+* inspired by https://github.com/TACC/Core-Portal/pull/1018#pullrequestreview-2476250609
+
+## Changes
+
+**`.dropdown-menu`**:
+- remove redundant code
+- use `<Dropdown>` not `<ButtonDropdown>`[^1]
+- clean up styles
+- use CSS var's for arrow and border
+
+**`DataFilesBreadcrumbs`**:
+- fix layout of menu and button
+
+**`DataFilesBreadcrumbs`**:
+- use class not ID
+- position via `top` not `margin-top`
+- explain menu position value
+- explain why positioning is necessary[^2]
+
+[^1]: I don't see `ButtonDropdown` in [latest ReactStrap (v9)](https://reactstrap.github.io/?path=/docs/components-dropdown--dropdown).
+[^2]: Not desired, but necessary if we use our custom `<Button>` as is.
+
+## Testing
+
+1. Open Data Files.
+2. Click "Add +" button.
+    - Verify button is centered.
+    - Verify menu is centered.
+    - Verify menu is wider than button.
+    - Verify elements are otherwise unchanged.
+4. Click "Go to ..." button.
+    - Verify elements are unchanged.
+
+## UI
+
+| `DataFilesDropdown` | `DataFilesSidebar` |
+| - | - |
+| <img width="400" alt="DataFilesDropdown" src="https://github.com/user-attachments/assets/c0a35d5b-d304-4625-b94e-6ab7888ec3e4"> | <img width="400" alt="DataFilesSidebar" src="https://github.com/user-attachments/assets/7bec0d60-ec77-45d7-b53d-7c0688d8c75b"> |
+
+## Notes
+