fonts on table view headers enormous on Windows

I am trying to deploy a solution I built on a Mac to some windows users, and the UI has become unusable in Windows.

The problem is the headers on Table View forms (in Smart client) are a much bigger font than they are on the Mac, or than they should be.

I have had a look through the CSS and hoped that this bit might allow me to change the styling:

/*

  • Example of additional grid styling (Portals and TableViews)
  • The gridheader and gridcell style classes needs to be set on resp. the header labels and the cell elements of TableView’s and Portals
    */
    label.gridheader
    field.gridcell,
    check.gridcell,
    radio.gridcell,
    combobox.gridcell,
    label.gridcell

However changing the font size there (like this:

label.gridheader{
font-size: 10px;
}

field.gridcell,
check.gridcell,
radio.gridcell,
combobox.gridcell,
label.gridcell

) does not make any difference…

What am I missing?

Thanks

Bevil