How could I improve the design?
I have already an idea for the microphone design so I’ll leave it for later for the moment.
This web page main idea is that there is a bot you can talk to and ask something both using the microphone or typing messages in the live chat box to show what type of data you want to be showed on the d3.js graph.
Hello! One thing you could do is combine all three buttons (Record, Start,Stop) into one <div> and put it just below the microphone icon ( that you could also improve by centering it in the block). Also, one possible thing for you to do is to change colors of the buttons in accordance to your messages’ colors in the chat ( make the buttons’ borders rounded( border-radius: 10%; ) and the set background colors like dodgerblue, lightgreen and so on.)
Also, there is no need for such large spaces dedicated to messages, you could resize them a bit. 
