Make .dynamic-buttons have width: 100%
Make .dynamic-buttons have width: 100%

- Make .dynamic-buttons expand to fill horizontal space to render better on smaller screens.
- Currently, .dynamic-buttons is hard-coded to width: 400px.
- This mostly works; however, when there are many dynamic buttons (e.g., when you select a Python file) the 400px width causes overflow to another line.
dunovank/jupyter-themes,dunovank/jupyter-themes,dunovank/jupyter-themes