Grid footer/header cell setStyleName() not working

i am trying to style up the header and footer section of the grid (Framework 7)
sample below:

Grid.FooterRow fr = mygrid.appendFooterRow();
Grid.FooterCell fc = fr.getCell(PropertyId);

.v-grid-cell.red_bk {
background-color: red;

not giving any results, any idea please
Thank You very Much

The method you have tried works with some things, e.g. if you would set bold font weight or text color, it will work. But for background color it is not working, use this Valo variable to set background color of Grid header in your theme .scss file.

$v-grid-header-background-color: red;

yes, works fine thank you