Responsive Web Design: Added hint to Add Borders Around Your Elements (#19589)

Added hint to Add Borders Around Your Elements (https://learn.freecodecamp.org/responsive-web-design/basic-css/add-borders-around-your-elements)

guide/english/certifications/responsive-web-design/basic-css/add-borders-around-your-elements/index.md

@@ -2,9 +2,32 @@
 title: Add Borders Around Your Elements
 ---
 ## Add Borders Around Your Elements
-
-This is a stub. <a href='https://github.com/freecodecamp/guides/tree/master/src/pages/certifications/responsive-web-design/basic-css/add-borders-around-your-elements/index.md' target='_blank' rel='nofollow'>Help our community expand it</a>.
-
-<a href='https://github.com/freecodecamp/guides/blob/master/README.md' target='_blank' rel='nofollow'>This quick style guide will help ensure your pull request gets accepted</a>.
-
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+
+We need to create a class called ```thick-green-border```. This class should add a 10px, solid, green border around an HTML element. and after, we need to apply the class to your cat photo.
+
+## Solution:
+
+We add between ```<style>``` and ```</style>``` new class ```thick-green-border``` with properties:
+
+```js
+  .thick-green-border {
+    border-color: green;
+    border-width: 10px;
+    border-style: solid;
+  }
+```
+Also, we can add properties this way:
+
+```js
+  .thick-green-border {
+    border: 10px solid green;
+  }
+```
+The final stage is adding this class to image:
+
+```js
+<img class="smaller-image thick-green-border" 
+src="https://bit.ly/fcc-relaxing-cat" 
+alt="A cute orange cat lying on its back.">
+```