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

Yes

The word "descansar" is identical in meaning, grammar, and spelling in both Brazilian and Continental Portuguese. The only difference lies in pronunciation. In Brazil, the "s" is pronounced as a soft [s], and the final "r" is often aspirated (sounding like an "h") or dropped entirely in casual speech (e.g., "descansá"). In Portugal, the "s" is more sharply sibilant, and the vowels tend to be more closed and less nasalized than in Brazil.

Brazilian Portuguese Examples

1. Eu preciso descansar um pouco depois do trabalho. (I need to rest a bit after work.)
2. Eu estou descansando no sofá agora. (I am resting on the sofa right now.)
3. A gente vai descansar na praia no fim de semana. (We are going to rest at the beach on the weekend.)
4. Você não pode descansar tanto assim! (You can't rest that much!)
5. Ele só quer descansar e esquecer os problemas. (He just wants to rest and forget his problems.)

Portuguese (Continental) Examples

1. Eu preciso de descansar um pouco depois do trabalho. (I need to rest a bit after work.)
2. Eu estou a descansar no sofá agora. (I am resting on the sofa right now.)
3. Nós vamos descansar na praia ao fim de semana. (We are going to rest at the beach on the weekend.)
4. Tu não podes descansar tanto assim! (You cannot rest that much!)
5. Ele só quer descansar e esquecer os problemas. (He just wants to rest and forget his problems.)