That’s one of many lessons the Republican National Committee’s digital experiment team learned in 2016 while testing and retesting everything about the Trump campaign’s website, down to the color of the “donate” buttons, according to a new report prepared by the RNC. The report estimates that the testing program run by the RNC’s Performance Optimization and Experiments Team — POET for short — brought in over $30 million extra to the Trump campaign by boosting its digital engagement and fundraising.

“The dynamic nature of the Donald J. Trump Presidential Campaign presented us with a wealth of copy, images and myriad digital assets,” wrote the report authors, a combination of RNC digital operatives and consultants with Giles-Parscale, Trump’s online consulting firm. “Our objective: find out how to best package and deliver our content to best engage potential.”

The best practices included using pictures of Trump with his thumbs up above practically all else for fundraising asks on his campaign website.