Is the word costas the same in Brazilian and European Portuguese?

Yes

The word "costas" is identical in meaning, grammar, and spelling in both Brazilian and Continental Portuguese. It refers to the anatomical back (human or animal) or the back side of an object. The only difference is in pronunciation. In Brazilian Portuguese, the vowels are more open and the final "as" is clearly articulated. In Continental Portuguese, the vowels are often more closed or reduced, and the rhythm of the word follows the distinct stress patterns of European Portuguese.

Brazilian Portuguese Examples

1. Minhas costas estão doendo muito hoje. (My back is hurting a lot today.)

2. Ele carregou a mochila pesada nas costas. (He carried the heavy backpack on his back.)

3. Ela tem uma tatuagem linda nas costas. (She has a beautiful tattoo on her back.)

4. Fique de costas para a porta, por favor. (Turn your back to the door, please.)

5. Senti um peso nas costas depois do treino. (I felt a weight on my back after the workout.)

Continental Portuguese Examples

1. Estou com dores nas costas. (I have back pains.)

2. Ele levava a mochila às costas. (He was carrying the backpack on his back. Note: "Às costas" is a very common way to express this in Portugal.)

3. Ela tem uma tatuagem bonita nas costas. (She has a beautiful tattoo on her back.)

4. Fica de costas para a câmara. (Stay with your back to the camera. Note: "Câmara" is the standard spelling in Portugal.)

5. A mochila pesa muito às costas. (The backpack is very heavy on the back.)