Try this:
css='''
[data-testid="metric-container"] {
width: fit-content;
margin: auto;
}
[data-testid="metric-container"] > div {
width: fit-content;
margin: auto;
}
[data-testid="metric-container"] label {
width: fit-content;
margin: auto;
}
'''
# I usually dump any scripts at the bottom of the page to avoid adding unwanted blank lines
st.markdown(f'<style>{css}</style>',unsafe_allow_html=True)