The HTML/CSS widget or text widget gives you the option to present a (designed) text in your dashboard. In some cases you want to present some context to the users that are going to view the dashboard. With the HTML text widget you can present additional information, an introduction or explanation about the dashboard or for example periodical feedback to your team. 

There is no need to actually have knowledge of HTML/CSS. With the editor mode you can use this widget the same way you would use a text editor. If you do choose to use the HTML/CSS option you can design it in any style that you want. A simple explanatory text now blends in perfectly and becomes part of your dashboard. Some examples:

You can find this versatile widget under the Normal widgets > General section > HTML Editor/Text Editor.