Add classes

All classes **must** be explicit because this will make easy
to translate the lessons.

01-one.md

@@ -4,7 +4,7 @@ title: Lesson Title
 subtitle: Topic Title One
 minutes: 10
 ---
-> ## Learning Objectives
+> ## Learning Objectives {.objectives}
 >
 > * Learning objective 1
 > * Learning objective 2

02-two.md

@@ -4,7 +4,7 @@ title: Lesson Title
 subtitle: Topic Title Two
 minutes: 10
 ---
-> ## Learning Objectives
+> ## Learning Objectives {.objectives}
 >
 > * Learning objective 1
 > * Learning objective 2

LAYOUT.md

@@ -167,7 +167,7 @@ Each topic page must be structured as follows:
     subtitle: Topic Title
     minutes: 10
     ---
-    > ## Learning Objectives
+    > ## Learning Objectives {.objectives}
     >
     > * Learning objective 1
     > * Learning objective 2

index.md

@@ -4,7 +4,7 @@ title: Lesson Title
 ---
 Paragraph of introductory material.
 
-> ## Prerequisites
+> ## Prerequisites {.prereq}
 >
 > A short paragraph describing what learners need to know
 > before tackling this lesson.