CSS: Add ::after pseudo-element document (#19381)

I noticed most of the pseudo-selectors/pseudo-elements are missing from this section, so I created a basic document as a starting point for the ::after pseudo-element. I tried to follow the same layout and style as the other articles in this section. This document is meant to be a start and added to/expounded on.

It's also my first real pull request - so please let me know how I can improve if needed 👍

client/src/pages/guide/english/css/selectors/pseudo/after/index.md

@@ -0,0 +1,42 @@
+---
+title: After
+---
+## After
+
+The ```::after``` CSS pseudo-element inserts a custom HTML element after the content of the selected HTML element. This selector is most commonly used to add visual content using the CSS ```content``` property.
+
+General Syntax:
+
+```css
+::after
+```
+
+## Example
+
+```css
+/* "Text to insert" is placed after the content of each <div> element */
+div::after {
+  content: "Text to insert";
+}
+```
+
+## More Examples
+
+A great example of a practical use case is if you wanted to display the ```href``` attribute value for all links on your page.
+
+```html
+<a href="www.freecodecamp.org">Learn to code</a>
+```
+
+```css
+a::after {
+  content: " " attr(href);
+}
+```
+
+The ```::after``` CSS pseudo-element can be used in many creative ways, especially when combined with it's sibling ```::before```.
+
+#### More Information:
+* [MDN Web Docs](https://developer.mozilla.org/en-US/docs/Web/CSS/::after)
+* [W3 Schools](https://www.w3schools.com/cssref/sel_after.asp)
+* [CSS Tricks - A Whole Bunch of Amazing Stuff Pseudo Elements Can Do](https://css-tricks.com/pseudo-element-roundup/)