Depends if you're using markdown or the "Fancy Pants Editor". In Markdown you simply put a > at the start of the paragraph, like this:

>This is a quote

In the "Fancy Pants Editor" you have to select the quote block option through the GUI.

>So where does this mass come from in the fusion process?

The product has less mass than the ingredients. Mass is being lost, not gained, so the question is where does the mass go.

The answer to where the mass goes is that it goes to the energy of the radiation being emitted.

> Neutrons are > slightly > more massive than protons, so all things being equal you can understand why 1 helium should have > slightly > more mass than 4 hydrogens.

Actually, the helium produced in the proton-proton chain has less mass than the constituent hydrogens. The difference is about 23 MeV, which goes into the mass and energy of the byproducts (neutrinos and gamma radiation).

This answer is wrong. Deuterium and tritium are just as much hydrogen as protium is, and similarly helium includes helium-3 as well as helium-4. Further, deuterium has a mass of 2,014,101.777844 µu, while helium-4 has a mass of 4,002,603.254130 µu, so we can see that even when the number of protons and neutrons line up, the mass is not the same.

As you can see from the numbers I just posted, you and OP (u/TheLapisBee) are actually also backwards in that 2 ^(2)H atoms have more mass than 1 ^(4)He atom.