Update solutions.md

Adding a solution for the cascade example.

Author: rachelandrew

learn/solutions.md

@@ -2,6 +2,24 @@
 
 Solutions for the tasks in the CSS Learn section of MDN.
 
+## The Cascade
+
+[Task](https://developer.mozilla.org/en-US/docs/User:chrisdavidmills/CSS_Learn/Cascade_and_inheritance#Active_learning_playing_with_the_cascade)
+
+Task: Write a declaration in a new rule that will reset the background color back to white, without using an actual color value?
+
+One possible solution is as follows:
+
+```
+#outer #inner a {
+  background-color: initial;
+}
+```
+
+There are two things you need to do in this task. First, you need to write a selector for the `a` element which is more specific than the selector used to turn the background blue. I have achieved this by using the `id` selector which has very high specificity. 
+
+Then you need to remember that there are special keyword values for all properties. In this case I am using `inherit` to set the background back to be the same as its parent element.
+
 ## Attribute Selectors
 
 [Task](https://developer.mozilla.org/en-US/docs/User:chrisdavidmills/CSS_Learn/CSS_Selectors/Attribute_selectors#Try_it_out)
@@ -56,4 +74,4 @@ h2 {
   background-color: rgba(0,0,0,.5);
   color: white;
 }
-```
+```