  We review the main results obtained from our seismic studies of B-type main
sequence pulsators, based on the ground-based, MOST, Kepler and BRITE
observations. Important constraints on stellar opacities, convective
overshooting and rotation are derived. In each studied case, a significant
modification of the opacity profile at the depths corresponding to the
temperature range $\log{T}\in (5.0-5.5)$ is indispensable to explain all
pulsational properties. In particular, a huge amount of opacity (at least
200\%) at the depth of the temperature $\log T = 5.46$ (the "nickel" opacity)
has to be added in early B-type stellar models to account for low frequencies
which correspond to high-order g modes. The values of the overshooting
parameter, $\alpha_{\rm ov}$, from our seismic studies is below 0.3. In the
case of a few stars, the deeper interiors have to rotate faster to get the
g-mode instability in the whole observed range.
