While posting an answer on UX.stack (then moved to Graphic Design) I found out I wasn't sure about how to express this:
The Go button size should be bigger and present the best contrast of all since it's the primary one.
1) Is present used correctly? Should I have used another verb instead?
2) Is best the correct adjective for contrast, or would highest be better?
3) Is there anything else to correct in the sentence?
I would say this as:
The Go button should be the largest element and should have higher contrast since it is the primary element on the screen.
However, your sentence structure is also fine. As noted in the comments, you can change out the word best for any of the following:
Your word present would sound more natural as just have. Or you could (following suggestions in the comments), use contrast as a verb.
To summarize, any of the following sentences would work:
The Go button should be the largest element and should have higher contrast since it is the primary element on the screen.
The Go button size should be bigger and have the highest contrast of all, since it's the primary one.
The Go button size should be bigger and contrast most strongly, since it's the primary one.