On a museum website, you can zero in on the details of the painting. You can see where he put the background around the flowers. The flowers are just a stroke of the brush. You can also see how he simplified the greenery and the shrubbery. He just used strokes of paint rather than putting in any detail.
Also, rather than using shadows, he creates interest by the contrast of the intense foreground against the soft background—and by outlining where the two cross. Around the leaves and flowers and even the vase, you can see the soft black lines he used to make them stand off from the background.
My basic sketch is outlined in black (technically phthalocyanine blue). I used the leaves as my outline because they’re so dark in the original. I relied more on the leaves, less on the flowers themselves. He has a lot of variations of color in there, a little bit of purple in there, and I wanted to get it right.