Using the Style function with Slot (#), Function(&) and Map (/@)

    headers = Style[#, {FontFamily -> "Arial", FontSize -> 20}] & /@ {"A", "B", "C"}
    Grid[Prepend[{{g, g, g}}, headers]]

[![enter image description here][1]][1]


  [1]: https://i.sstatic.net/NX61l.png