Envelope accretion-driven evolution of the density distribution of a representative ETG. Initial (dashed curves), accreted (dotted curves), and final (solid curves) stellar (red curves) and DM (black and grey curves) density profiles of our reference model galaxy growing via envelope accretion. The vertical lines indicate the initial ($R_{\mathrm{e}}^{\mathrm{initial}}$) and final ($R_{\mathrm{e}}^{\mathrm{final}}$) effective radii. ${\rho }_{\star ,\mathrm{e}}^{\mathrm{initial}}$ is the initial stellar density at $r=R_{\mathrm{e}}^{\mathrm{initial}}$.