  We compare mock ultraviolet C II and Si II absorption and emission line
features generated using a ~10$^9$ $M_\odot$ virtual galaxy with observations
of 131 $z~3$ galaxies from the VANDELS survey. We find that the mock spectra
reproduce reasonably well a large majority (83%) of the \vandels\ spectra
($\chi^2<2$), but do not resemble the most massive objects ($>10^{10}M_\odot$)
which exhibit broad absorption features. Interestingly, the best-matching mock
spectra originate from periods of intense star formation in the virtual galaxy,
where its luminosity is four times higher than in periods of relative
quiescence. Furthermore, for each galaxy, we predict the Lyman Continuum (LyC)
escape fractions using the environment of the virtual galaxy. We derive an
average escape fraction of 0.01$\pm$0.02, consistent with other estimates from
the literature. The predicted escape fractions are tightly correlated with the
Lyman-$\alpha$ escape fractions and highly consistent with observed empirical
trends. Additionally, galaxies with larger predicted escape fractions exhibit
bluer $\beta$ slopes, more Lyman-$\alpha$ flux, and weaker low-ionization
absorption lines. Building upon the good agreement between our predictions and
observationally established LyC diagnostics, we examine the LyC leakage
mechanisms in the simulation. We find that LyC photon leakage is enhanced in
directions where the observed flux dominantly emerges from compact regions
depleted of neutral gas and dust, mirroring the scenario inferred from
observational data. In general, this study further highlights the potential of
high-resolution radiation hydrodynamics simulations in analyzing UV absorption
and emission line features and providing valuable insights into the LyC leakage
of star-forming galaxies.
