Was complete and utter nothingness.
In some versions of the myth Chaos was nothing but the primordial void from which everything came to be. So imagine blackness. And then poof. Things. That was Chaos. Sometimes, Chaos did appear as a goddess in some very, very underground mythology. For the most part Chaos was nothingness. The blank page. The clean slate that somehow farted out deities and the world (in some versions Chaos literally gave birth to Nyx and Erebos). No idea how that worked but we’ll roll with it.