The velocity of electromagnetic wave is parallel to : -

In an electromagnetic wave, $\vec{E}$ and $\vec{B}$ are perpendicular to each other and to the direction of propagation.
The direction of propagation (and of energy flow, the Poynting vector) is along $\vec{E} \times \vec{B}$.

Example: if $\vec{E}$ is along $\hat{i}$ and $\vec{B}$ along $\hat{j}$, the wave travels along $\hat{i} \times \hat{j} = \hat{k}$.
So the velocity of an electromagnetic wave is parallel to $\vec{E} \times \vec{B}$.