Notice that to minimize the loss (red box) you move the above sliders in the direction that makes the box smaller. This direction is the negative of the gradient. In practice, experts at this game might move each slider to its minimum and then move the next slider. This procedure is actually called coordinate descent and is another commonly used algorithm for minimizing the loss.
Professor Gonzalez is bad at web design so if you want to make this game the award winning game it should be please send us a pull request: Github Link.