What is the mechanism for atoms absorbing light? Apart from saying that electron orbitals have specific energy levels and can only absorb light of that energy/wavelength, what actually causes electrons to absorb the energy?
 A: 
Apart from saying that electron orbitals have specific energy levels and can only absorb light of that energy/wavelength,

Please note that we call them electron orbitals because we assume a framework where the  nucleus is at rest. They are actually "atomic orbitals" It is the whole atom that changes in energy when a photon is absorbed.

what actually causes electrons to absorb the energy?

Electrons do not absorb energy. The atom does, and the electron is raised into a higher energy orbital. The cause is the impinging of a photon that carries the energy packet that separates the two orbitals.
A: Fundamentally, the process responsible for the absorption / emission of a photon is expressed in the Hamiltonian coupling the field to the atom, that is
$$
H=-\bf{d.E}
$$
so it is the the field-dipole interaction which is at stake here, and it is this interaction that dictates the selection rules for the transitions.
A: I think the electrons requires energy to transit into higher energy level...
Because energy changes when we move from one orbit to another
