Customize Web App Popups

[Wasserwiki]

I only recently started working with ArcGis Online. It perfectly fits my needs so far, but is there any way to customize the style of a popup in Arc Gis Online Map Viewer or Arc Gis Online Web App Builder? I specified the content via the regular Map Viewer. But now I'd like to customize f.e. color and size of the popups. Is this possible?

[JohannesLindner]

You can change the color of the popup window's top bar (Web AppBuilder -> Design -> Style).

To change the window's size and border colors, you need javascript. I don't think you can change that in the Map Viewer or the Web AppBuilder.

You can use HTML to style the content of the popup, though. While configuring the popup in the Map Viewer, change to HTML source:

[Wasserwiki]

Thanks Johannes!

So for customizing the pop up I could download the webapp and edit the specific files and upload it afterwards on my webserver to display the custom version?

Would this be the way to go?