[Vuejs]-Vuetify's datepicker doesn't show the dates

Assuming that you are using latest version of browser and all other browser related configurations are correctly configured, You may want to check other dependencies of the project for conflicting CSS elements, which is resulting in wrong CSSrendering.

If it works in Codepen then I would check the version of the Vuetify on your end and the version of that in Codepen. It might be that your are using the older version of Vuetify that does not fully support DatePicker.