Update 21_day_dom.md

Edit by class name would be 3

21_Day_DOM/21_day_dom.md

@@ -105,7 +105,7 @@ document.getElementsByClassName('classname')
 const allTitles = document.getElementsByClassName('title')
 
 console.log(allTitles) //HTMLCollections
-console.log(allTitles.length) // 4
+console.log(allTitles.length) // 3
 
 for (let i = 0; i < allTitles.length; i++) {
   console.log(allTitles[i]) // prints each elements in the HTMLCollection