To add code to a style, navigate to:
  1. onMessage > Website > Site Name
  2. Styles
  3. Edit the appropriate style
  4. Change the Default dropdown to Content Types
  5. Click the Text icon (T)
  6. Click on the section under Header
  7. On the bottom lefthand side, select Advanced CSS
  8. Choose Content from the dropdown and add this code within the CSS:
width: 100%;
height: 100%;
overflow: scroll;
​       9. Apply Changes