st.line_chart is a quick-start/convenience function for getting started creating plots, and as such, doesn’t have any arguments to it. When you want to customize the chart further, st.line_chart is a wrapper around st.altair_chart, which gives you the full power of the Altair plotting library.
Thanks for your reply, I suspected that and got it working with something like:
c = alt.Chart(dataframe).mark_line().encode(x='index', y = alt.Y('Close', scale=alt.Scale(zero=False))).properties(width=800, height=150)
st.altair_chart(c)
(it would however be nice to have this “zero=False” in st.line_chart).