The phrase "Happy Easter with theme books" is almost correct, but to make it clearer and grammatically better, you could say:
- "Happy Easter with themed books!" — This means you are wishing someone a Happy Easter and mentioning books that have an Easter theme.
- Or, "Happy Easter with Easter-themed books!" — This is even clearer because it specifies the books are about Easter.
So, the corrected and improved phrase could be "Happy Easter with Easter-themed books!"
Remember, "theme books" sounds a little incomplete, so adding "themed" or specifying the theme helps make the sentence clearer.