"Design a thumbnail that captures the concept of mental balance and peace through a photorealistic image of a rock cairn by a tranquil river. The carefully balanced stones reflect the delicate balance of mental health, symbolizing stability and mindfulness. The background should feature the gentle flow of the river and surrounding nature in soft, calming colors, emphasizing serenity and the steady flow of life, chaos, 4k --ar 16:9 --niji 6