As we see here variation is happening we know that the fox is only interested in the light brown mice.
We know that all the mice are trying to survive especially the light brown ones this is called struggling to survive.
We see here survival we see the dark brown ones were the ones that survived and the fox didn't find the dark browns ones because they camouflage with there environment.
These brown mice are now going to pass on their genes and now reproduce. They're most likely to survive because they mix in into there surroundings and the population would be more brown mice than white mice.