TL;DR our version of [HIG's
Box](https://developer.apple.com/design/human-interface-guidelines/boxes)
We can't use the name `Box` (because rust) or `ContentBox` (because
taffy/styles/css).
---
This PR introduces the `ContentGroup` component, a flexible container
inspired by HIG's `Box` component. It's designed to hold and organize
various UI elements with options to toggle borders and background fills.
**Example usage**:
```rust
ContentGroup::new()
.flex_1()
.items_center()
.justify_center()
.h_48()
.child(Label::new("Flexible ContentBox"))
```
Here are some configurations:
- Default: Includes both border and fill.
- Borderless: No border for a clean look.
- Unfilled: No background fill for a transparent appearance.
**Preview**:
---
_This PR was written by a large language model with input from the
author._
Release Notes:
- N/A
04ba75e2e5