Rather than trying to apply some css you could use some jQuery to perform this task. I do something similar in terms of height. So maybe something like this would work for you (I have modified this to do height and width).
function resizeGrid(size) {
if (size === null || size === undefined) {
size = 0.6;
}
var windowHeight = $(window).height();
var windowWidth = $(window).width();
windowHeight = windowHeight * size;
windowWidth = windowWidth * size;
$(".k-grid-content").height(windowHeight)
$(".k-grid).width(windowWidth);
}
so all this function does is scale the grid based on the current window size so for example if you want the grid to take up all the available space ie max height and width you would call resizeGrid(1)
if you wanted it smaller say to take 50% of the screen size then you would use reszieGrid(0.5)
if no value is used then the function just goes with a default of 60% of the available width/height.
so you could call this after your initialization of the grid and then scale the grid to an appropriate size.
by targeting the kendo css classes it makes this function easier to reuse.
if you need more info let me know.