You can refer conditional-format.php demo in archive (demos/appearance)

// if nothing set in 'op' and 'value', it will set column formatting for all cell
$f = array();
$f["column"] = "invdate";
$f["css"] = "'background-color':'#FBEC88', 'color':'green', 'font-weight':'bold'"; // must use (single quote ') with css attr and value
$f_conditions[] = $f;

$g->set_conditional_css($f_conditions);

If I lock first column (witch should be formatted) happens this:

Column Formatting is not supported with frozen column and it's known limitation of frozen column function.