You can using the CSS in markdown hack, you can basically put CSS in the app and unsafe_allow_html to True in st.markdown to have it parsed (as long as your CSS selectors are specific enough to point to the correct widget everything is possible), some examples in the following :
- Creating a nicely formatted search field? - #2 by andfanilo
- Changing color of a column - #3 by andfanilo
- Can I change the color of the selectbox widget? - #2 by andfanilo
Fanilo