According to the prevailing understanding in particle physics, quarks and leptons are considered to be elementary particles, meaning they are not composed of smaller constituents. As far as our current knowledge and experimental evidence indicate, quarks and leptons are indivisible and point-like entities.
Quarks are the fundamental particles that experience the strong force, which is mediated by gluons. They come in six flavors: up, down, charm, strange, top, and bottom. Each flavor of quark carries an electric charge and participates in the weak and electromagnetic interactions as well.
Leptons, on the other hand, do not experience the strong force. There are six known leptons: the electron, muon, tau, and their corresponding neutrinos. Leptons also carry electric charge and interact through the weak and electromagnetic forces.
Extensive experimental investigations, such as high-energy particle collisions and scattering experiments, have probed the internal structure of quarks and leptons. Thus far, no evidence of substructure or composite nature has been found. These particles are considered to be point-like and structureless at the energy scales we have been able to explore.
However, it is important to note that our understanding of particle physics is continuously evolving. New experiments or theoretical breakthroughs might reveal previously unknown substructure or deeper levels of complexity within quarks and leptons. For now, based on the available evidence, they are treated as elementary particles.