You can change the display of Roundcube by changing its theme.
Access to the Webmail
Task completion: 2 minutes (max)
How to do it?
Connect to Roundcube Webmail
Once connected to Roundcube go to Settings
On the new page click on Preferences > User interface
Now under Interface skin, you have the choice between Elastic and Larry
a) Larry is the classic Roundcube theme
b) Elastic is Roundcube's new modern theme
Select the theme you want and Save the changes