"Minimalistic digital collectible card for a fitness-themed mobile app. The card features a clean and simple border with soft pastel tones (e.g., light blue and white) and rounded edges. At the center, an illustration of a person performing a fitness exercise, such as a plank or squats, with smooth, minimal line art and a flat design style. The title 'Plank Challenge' is displayed below in clean sans-serif typography. The background is a subtle gradient or solid color, ensuring a fresh and modern appearance. Avoid heavy details or futuristic elements; focus on simplicity, clarity, and elegance."