I'm reading QISKIT documentation. https://qiskit.org/textbook/ch-gates/multiple-qubits-entangled-states.html#3.2-Entangled-States- and they show qbits entangled as |00> (both qbits spin down) or |11> (both qbits spin up). Also written as

1 / √ 2 ( | 00 ⟩ + | 11 ⟩ )

From my understanding, entanglement requires one particle to be spin up and the other spin down. How is the above entangled state possible?