Update app.py

app.py

@@ -52,8 +52,8 @@ st.sidebar.header("Contents")
 st.sidebar.markdown("""
 - [Introduction](#Introduction-to-Machine-Learning-ML)""")
 # Nested sidebar for "Types of Machine Learning"
-with st.sidebar.expander("Types of Machine Learning"):
-    st.markdown("""
+st.sidebar.header("Types of Machine Learning")
+st.markdown("""
     - [Supervised Learning](#Supervised-Learning)
     - [Unsupervised Learning](#Unsupervised-Learning)
     - [Reinforcement Learning](#Reinforcement-Learning)