Merge pull request #5528 from lldelisle/third_way_to_run_DESeq2

Fix CYOA of collection split in Ref-based

topics/transcriptomics/tutorials/ref-based/tutorial.md

@@ -1576,7 +1576,7 @@ We can now run **DESeq2**:
 {: .hands_on}
 
 </div>
-<div class="Collection split" markdown="1">
+<div class="Collection-split" markdown="1">
 
 DESeq2 requires to provide for each factor, counts of samples in each category. We will thus use patterns on the name of our samples to easily select all samples belonging to the same category.