Although the standard model (SM) is extremely successful, there are various motivations for considering the physics beyond the SM. For example, the SM includes neither dark energy nor dark matter, which has been confirmed through astrophysical observations. Examination of the dark sector, which contains new, light, weakly-coupled particles at the GeV scale or lower, is well motivated by both theory and dark-matter detection experiments. In this mini-review, we focus on one particular case in which these new particles can interact with SM particles through a kinematic mixing term between U(1) gauge bosons. The magnitude of the mixing can be parameterized by a parameter ϵ. Following a brief overview of the relevant motivations and the constraints determined from numerous experiments, we focus on the light dark sector phenomenology at low-energy high-luminosity e⁺e⁻ colliders. These colliders are ideal for probing the new light particles, because of their large production rates and capacity for precise resonance reconstruction. Depending on the details of a given model, the typical observed signatures may also contain multi lepton pairs, displaced vertices, and/or missing energy. Through the use of extremely large data samples from existing experiments, such as KLOE, CLEO, BABAR, Belle, and BESIII, the ϵ<10⁻⁴–10⁻³ constraint can be obtained. Obviously, future experiments with larger datasets will provide opportunities for the discovery of new particles in the dark sector, or for stricter upper limits on ϵ. Once the light dark sector is confirmed, the particle physics landscape will be changed significantly.