Dialog
Dialog is a transient UI element which appears when something happens that requires notification, approval, or additional information from the user. Dialogs block interactions with the app window until being explicitly dismissed. They often request some kind of action from the user. Mixed Reality Design Labs' Dialog provides one or two button options.
You can find the samples in the scene SimpleDialog_Examples.unity under https://github.com/Microsoft/MRDesignLabs_Unity/tree/master/DesignLabs_Unity_Examples/Assets/MRDL_ControlsExample/Scenes