How to change the css when the mouse move over the grid(Only a grid)

I try to change the .x-grid-row-over .x-grid-cell-inner

but this change all the component not only the grid,

and i try to change like this ,but not word

in the my_css.css

.my_test_css {

font-weight: bold;

background-color:#00FF00 !important;

color: green;

}

in the grid set me.overCls = 'my_test_css';

Somebody know how to config this css?