Put videos links in subjects.

subjects/action-reaction/README.md

@@ -30,9 +30,7 @@ In the JS file, get the HTML button element with [`querySelector`](https://devel
 
 ### Expected output
 
-This is what you should see in the browser:
-
-<!-- screenshot -->
+[This](https://youtu.be/Wkar5SmswDo) is what you should see in the browser.
 
 ### Notions
 

subjects/bring-it-to-life/README.md

@@ -9,7 +9,7 @@ First, define this new class in your CSS file:
 
 ```
 .eye-closed {
-  height: 2px;
+  height: 4px;
   padding: 0 5px;
   border-radius: 10px;
 }

subjects/first-words/README.md

@@ -35,9 +35,7 @@ In the JS file, like in the previous exercise, get the HTML button element with
 
 ### Expected output
 
-This is what you should see in the browser:
-
-<!-- screenshot -->
+[This](https://youtu.be/Eq9liRCc-zA) is what you should see in the browser.
 
 ### Notions