Update CS0060 documentation

Improve the documentation for CS0060 to be clearer about the cause of the issue, and how it can be resolved. Also explain that types may be made less accessible while subtyping, as the previous doc suggested they had to be the same ("consistent").

Author: drewnoakes

docs/csharp/misc/cs0060.md

@@ -2,36 +2,39 @@
 description: "Compiler Error CS0060"
 title: "Compiler Error CS0060"
 ms.date: 07/20/2015
-f1_keywords: 
+f1_keywords:
   - "CS0060"
-helpviewer_keywords: 
+helpviewer_keywords:
   - "CS0060"
 ms.assetid: ae6d4fb7-5ff9-4883-82c3-f55b190f439a
 ---
 # Compiler Error CS0060
 
-Inconsistent accessibility: base class 'class1' is less accessible than class 'class2'  
-  
- Class accessibility should be consistent between the base class and inherited class.  
-  
- The following sample generates CS0060:  
-  
-```csharp  
-// CS0060.cs  
-class MyClass  
-// try the following line instead  
-// public class MyClass  
-{  
-}  
-  
-public class MyClass2 : MyClass   // CS0060  
-{  
-   public static void Main()  
-   {  
-   }  
-}  
-```  
-  
+Inconsistent accessibility: base class 'Class1' is less accessible than class 'Class2'
+
+In C#, a derived class cannot have broader accessibility than its base class. If the base class is less accessible, consumers of the derived class might unintentionally gain access to a class they shouldn't see.
+
+Subclasses may never be more accessible than their base classes. This would allow consumers of the subclass broader access to the base type than was intended.
+
+The following sample produces CS0060 because `Class1` is `internal` and `Class2` is `public`.
+
+```csharp
+internal class Class1
+{
+}
+
+public class Class2 : Class1 // 🛑 CS0060: Class1 is less accessible
+{
+}
+```
+
+You can resolve CS0060 in one of two ways:
+
+- Make the base class more accessible: Change `Class1` to be `public`.
+- Restrict the derived class's accessibility: Change `Class2` to be `internal`.
+
+Note that base classes may be _more_ accessible than their subclasses, but never _less_ accessible.
+
 ## See also
 
 - [Access Modifiers](../programming-guide/classes-and-structs/access-modifiers.md)