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From the Emacs help

C-x C— runs the command text-scale-adjust, which is an interactive autoloaded
Lisp function.

It is bound to C-x C-+, C-x C—, C-x C-=, C-x C-0.

(text-scale-adjust &optional INC)

Increase or decrease the height of the default face in the current buffer.

The actual adjustment made depends on the final component of the
key-binding used to invoke the command, with all modifiers removed:

+, = Increase the default face height by one step
- Decrease the default face height by one step
0 Reset the default face height to the global default

C-x C— is really, really close to C-x C-s on a Dvorak keyboard. If ever you hit it by accident, hit C-x C-0 to get your Emacs looking right.