How to fix the highlighter in the GridView that has some grouping rows?

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C#

ASP.NET

CSS

I am using a GridView that has many rows with the same values, so I grouped these rows using [GridViewHelper class][1]. Now I want to fix the highlighter since when the highlighter highlights the first row, for example, from the first three rows that are grouped in one cell in the first column, the highlighter will highlight the first cell, but when it highlights the second row, it doesn't highlight the first cell. WHY? and HOW TO FIX THAT?

The css code for the highlighter is:

.grid .datatable .row:hover
{
    background-color:#fffacd;
    color:#000;
}