Illustrate a minimalist username icon featuring a simple, bold letter 'U' with a subtle shadow effect, set against a clean white background, conveying a sense of simplicity and elegance.

Create a whimsical username icon featuring a cartoon character with a username written in bold, playful font, surrounded by confetti and balloons, conveying a sense of fun and celebration.

Design a futuristic username icon that incorporates a stylized letter 'U' with a subtle glow effect, surrounded by a circle with a subtle gradient effect, conveying a sense of modernity and technology.