Does DC voltage flow from positive to negative, or negative to positive?

Electron flow is from negative to positive. However, in analysis, it doesn't make any difference as long as you keep your signs correct. In engineering, often the flow of electricity is calculated going from positive to negative.

Voltage does not flow at all. By convention current flows from positive to negative although electrons are going from negative to positive (blame Ben Franklin and don't worry about it too much.)

FROM NEGATIVE TO POSITIVE !

THAT WAS A BIG MISTAKE MADE BY SCIENTISTS HUNDRED YEARS AGO THOUGHT IT WAS FROM POSITIVE TO NEGATIVE.