The green button on the left side of the title bar will Zoom that window. Zoom works something like Maximize on a PC, but it behaves differently.
Zoom makes the window "best size" for the screen. That means different things in different situations, but basically it means that the size of the window will increase or decrease just enough to make all of its parts visible. By contrast, Maximize on a PC makes a window go full screen.
Read this Q & A forum topic about Zooming a window to make it smaller.
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