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.