2. Use the color selector or gradient tool to select the gradient of green and blue as the background color.
3. Choose a suitable brush tool, such as watercolor pen or oil painting pen, and adjust the brush size and transparency.
4. With green as the bottom and blue as the top, lightly daub on the canvas with a brush tool to form a color transition effect.
5. Use different brush tools and colors in different positions of the canvas to increase the layering and richness of the picture.
6. You can add some decorative patterns or words in the center of the canvas or other suitable positions to make the whole background more vivid and interesting.
7. Finally, check the overall effect of the picture and adjust the details, color saturation and other parameters until the ideal effect is achieved.