The Grimm Brothers stories have themes like survival. In many tales, the characters have to survive in harsh conditions, such as the children in 'Hansel and Gretel' trying to survive in the forest and deal with the witch. Love is also a theme. In stories like 'Sleeping Beauty', love has the power to break the curse. Additionally, the theme of appearance versus reality can be seen. In some tales, things are not as they seem at first, like in 'The Bremen Town Musicians' where the old and seemingly useless animals turn out to be very useful.
One of the main themes is good versus evil. For example, in 'Snow White', the beautiful and kind Snow White represents good, while the jealous and cruel queen is evil. Another theme is transformation. In 'The Frog Prince', the prince is transformed into a frog and then back to his human form. Family also plays a role, like in 'Hansel and Gretel' where the siblings rely on each other in a difficult situation.
Well, magic is a big theme. There are lots of magical elements in the Grimm Brothers stories. Magic often helps the characters in their quests or causes trouble for them. Morality is also a theme. The stories teach lessons about right and wrong. For instance, in 'Cinderella', Cinderella's kindness is rewarded in the end. And there's the theme of the journey. Characters often go on journeys, both physical and emotional, like in 'Rapunzel' where Rapunzel has to endure a long time in the tower before her rescue.