The problem with a screenshot is the cursor doesn't show.

There's no visible "handle" like the hash-lines in the lower right corner of some windows (in my El Cap), but if I move my cursor to that corner - overlap the window and my desktop - the cursor turns into a diagonal two pointed arrow with which you can drag the window longer or wider.

The new Great Equalizer is the SEND button.

In Memory of Harv: Those who can make you believe absurdities can make you commit atrocities. ~Voltaire