What is a codex-style of painting ?

Its stylistic characteristics include fine-line painting using a monochrome black-brown slip (a clay-based paint pigmented with black iron oxide, manganese and/or plant-based compounds) applied on a light cream-colored background.
Variations in line tone achieved by degrees of dilution of the paint, red-painted rim and basal bands delimiting the pictorial field or page,and pictorial narratives featuring supernatural beings and classic myths.

∵they depict sad lonely people  ∵  figures in them have long limbs and faces, similiar in style to paintings by el greco.