How do I close down a window that does not have the red, yellow, and green buttons at the top corner?

Hey there! Most windows have the red, yellow, and green buttons at the top to minimize, maximize, or close down whatever window you're viewing. Some applications (for me, my college email) does not have that option once you maximize the window or even at all. I am wondering how i'm supposed to close that window down without having the quit my internet browser. Note: I have tried putting my cursor towards the top toolbar part of the screen and it still doesn't show those little buttons. It only shows the apple toolbar that has file, edit, view, etc. Thanks!