fix(guide): restructure curriculum guide articles (#36501)

* fix: restructure certifications guide articles
* fix: added 3 dashes line before prob expl
* fix: added 3 dashes line before hints
* fix: added 3 dashes line before solutions

guide/english/certifications/coding-interview-prep/data-structures/learn-how-a-stack-works/index.md

@@ -1,23 +1,30 @@
 ---
 title: Learn how a Stack Works
 ---
-## Learn how a Stack Works
+# Learn how a Stack Works
 
-### Method:
+---
+## Problem Explanation
 - Stacks are an abstract data structures.
 - They follow LIFO (Last In First Out) or FILO (First In Last Out) principle.
 - Stack's insertion and deletion operations are of **O(1)** time complexity.
 - In JavaScript, arrays can be treated as a Stack since `.push()` and `.pop()` methods have time complexity of **O(1)**.
 - In this challenge we need to `.pop()` and then `.push()` into the stack.
 
-### Solution:
+
+---
+## Solutions
+<details><summary>Solution 1 (Click to Show/Hide)</summary>
+
 ```js
-var homeworkStack = ["BIO12","HIS80","MAT122","PSY44"];
+var homeworkStack = ["BIO12", "HIS80", "MAT122", "PSY44"];
 
 homeworkStack.pop();
 homeworkStack.push("CS50");
 ```
-### Reference:
+#### Relevant Links
 
 - [Wikipedia](https://en.wikipedia.org/wiki/Stack_(abstract_data_type))
 - Video by [Hackerrank](https://www.youtube.com/watch?v=wjI1WNcIntg)
+
+</details>