Generally speaking, plastic packaging bags have things that are convex in the middle and concave on both sides. Look carefully at the picture you gave. There is an arc-shaped dark part on both sides. After you finish the picture of the plastic window, according to the analysis just now, fill the dark part with black, choose the superposition mode after proper blurring, and then reduce the transparency and feel it. Then add the dark sides of the upper and lower ends appropriately, and generally draw the lower part. The pictures you are looking for are all good examples. Analyze them carefully.
When the dark part is done, you can start to heighten the light. You can choose to draw a white line like a picture, or you can determine the bright area like a dark part, fill it with white and blur, and adjust the transparency in normal superposition mode.
Generally, the transparency should be adjusted to a relatively low ratio.
I hope this helps.