Access a class from Editor script? (Visual Studio)

I followed this unity docs tutorial: https://docs.unity3d.com/ScriptReference/Editor.OnSceneGUI.html

Placed DrawLineEditor within Editor folder. Placed DrawLine outside of Editor folder. Attached DrawLine to a GameObject, added some GameObjects to scene and registered them in DrawLine script via inspector. In unity, everything shows correctly.

After i opened the DrawLineEditor in VisualStudio, the VS reports error: "CS0246 The type or namespace name 'DrawLine' could not be found (are you missing a using directive or an assembly reference?)"

and all istances of "DrawLine" are red-underlined, showing error. How do i fix this in VisualStudio so that it recognizes "DrawLine" outside of the Editor folder? Namespaces dont seem to work either.