We have just redesigned Bitrix24 CRM details page - contact, lead, company, deal, etc. form. Since the new CRM Slider pane is in beta, you can switch it on from CRM Settings, or, in case you'd like to come back to the old one, disable it there as well.
To switch the new CRM Slider Pane please go to CRM > Settings > Other:
Scroll down to View Settings (under General tab) and activate Use Slider in viewer & editor: