Here’s some reading on Mendel’s Laws and non-Mendelian genetics; this is why I don’t use Mendel’s Laws when referencing linked genes or co-dominance.
Co-dominance is a direct violation of the Law of Dominance. Although it could be possible the allele are incomplete rather than co-dominant. You’d see this in flowers that can have different shades of pink from red and white parents, to use a simple example to match my co-dominance example of pink flowers.