Following Outer Circle Blue Color Border

Create a circular design with the following features:

1. Outer Circle: Use a bright blue color as the border instead of red.

2. Inner Circle: Maintain a solid black background.

3. Text: Replace "18+" with "21+" in a bold, white font, ensuring the numbers are large and centered.

4. Shape: Keep the overall circular shape but add a slight gradient to the blue border to give it depth.

5. Additional Element: Include a subtle pattern in the black background, such as faint diagonal stripes, to add texture.

This design should convey a similar message while incorporating the specified changes.