Understanding the chemical abundance of different elements in galaxies is crucial to gaining a complete picture of the interplay among gravitational potential well, star formation, and galactic outflows and inflows. In this talk, I will present our recently submitted paper on a new sample of 46 low-redshift, low-mass star-forming galaxies at 1e8-1e10 Msun along with two quiescent galaxies at M~1e8.8Msun observed with the Keck Cosmic Web Imager (KCWI), aiming to investigate the chemical evolution of galaxies in the transition zone between Local Group satellites and massive field galaxies. We develop a novel method to simultaneously determine stellar abundances of iron and magnesium in star-forming galaxies, enabling us to make the first-ever apples-to-apples comparison of alpha elements in the stars and the ISM. We find that [Mg/H]--[O/H] relation is much tighter than the [Fe/H]--[O/H], which can be a better indicator of the metal loss due to the outflows. In addition, we construct mass--metallicity relations measured as three elements (Fe, Mg, and O) and find that the Fe- and Mg-MZRs show larger scatter driven by different specific star formation rates than the O-MZRs, with star-forming galaxies exhibiting higher sSFR and lower stellar abundances at fixed mass. Most galaxies exhibit higher [O/H] than the stellar abundances, suggesting that the galaxy quenching of intermediate-mass galaxies at M*~1e8-1e10Msun is primarily driven by starvation.