Release Notes:
- N/A
---
Add this for let GPUI element to support fade in-out animation.
## Platform test
- [x] macOS
- [x] blade `cargo run -p gpui --example opacity --features macos-blade`
## Usage
```rs
div()
.opacity(0.5)
.bg(gpui::black())
.text_color(gpui::black())
.child("Hello world")
```
This will apply the `opacity` it self and all children to use `opacity`
value to render colors.
## Example
```
cargo run -p gpui --example opacity
cargo run -p gpui --example opacity --features macos-blade
```
<img width="612" alt="image"
src="https://github.com/user-attachments/assets/f1da87ed-31f5-4b55-a023-39e8ee1ba349">
