Overwriting the Header Style with Left Column Style in Table Styles

Hello! I'm trying to make a table style that makes my table look like the 2nd table in the image, but everything I've tried so far in table styles looks like the 1st table. Specifically, the issue I'm having is that the Top Left Cell of the table defined in the style uses the header style with the gray fill, but I want it to have no fill to match the rest of the left column, as well as no stroke on the left side of the cell. 

I've tried defining a cell style for the Header row and a separate cell style for the Left Column, but it seems the header cell style always overwrites the left column style. Even more bizzarre, one of my coworkers was able to create a table style that works like the 2nd table, but when we repeated the steps on my Mac they didn't work and gave me the 1st table. I'm just utterly confused on why this is happening. Does anyone know how I can define a table style to make the tables look like the 2nd table instead of the 1st?