feat(curriculum): adding content for pseudo-classes review page (freeCodeCamp#57046)

Author: jdwilkin4

client/i18n/locales/english/intro.json

@@ -1973,7 +1973,8 @@
       "review-css-pseudo-classes": {
         "title": "CSS Pseudo-classes Review",
         "intro": [
-          "Review the CSS Pseudo-classes concepts to prepare for the upcoming quiz."
+          "Before you are quizzed on CSS pseudo-classes and pseudo-elements, you first need to review.",
+          "Open up this page to review concepts like the <code>::before</code> and <code>::after</code> pseudo-elements as well as the <code>:hover</code>, <code>:active</code> pseudo-classes and more."
         ]
       },
       "quiz-css-pseudo-classes": {

curriculum/challenges/english/25-front-end-development/review-css-pseudo-classes/671a907bad4538752765f2ff.md

@@ -9,7 +9,94 @@ dashedName: review-css-pseudo-classes
 
 Review the concepts below to prepare for the upcoming quiz.
 
+## User Action Pseudo-classes
 
+- **Pseudo-classes Definition**: These are special CSS keywords that allow you to select an element based on its specific state or position.
+- **User Action Pseudo-classes**: These are special keywords that allow you to change the appearance of elements based on user interactions, improving the overall user experience.
+- **`:active` Pseudo-class**: This pseudo-class lets you select the active state of an element, like clicking on a button.
+- **`:hover` Pseudo-class**: This pseudo-class defines the hover state of an element.
+- **`:focus` Pseudo-class**: This pseudo-class applies styles when an element gains focus, typically through keyboard navigation or when a user clicks into a form input.
+- **`:focus-within` Pseudo-class**: This pseudo-class is used to apply styles to an element when it or any of its descendants have focus.
+
+## Input Pseudo-classes
+
+- **Input Pseudo-classes**: These pseudo-classes are used to target HTML `input` elements based on the state they are in before and after user interaction.
+- **`:enabled` Pseudo-class**: This pseudo-class is used to target form buttons or other elements that are currently enabled.
+- **`:disabled` Pseudo-class**: This pseudo-class lets you style an interactive element in disabled mode.
+- **`:checked` Pseudo-class**: This pseudo-class is used to indicate to the user that it is checked.
+- **`:valid` Pseudo-class**: This pseudo-class targets the input fields that meet the validation criteria.
+- **`:invalid` Pseudo-class**: This pseudo-class targets the input fields that do not meet the validation criteria.
+- **`:in-range` and `:out-of-range` Pseudo-classes**: These pseudo-classes applies styles to elements based on whether their values are within or outside specified range constraints.
+- **`:required` Pseudo-class**: This pseudo-class targets `input` elements that have the `required` attribute. It signals to the user that they must fill out the field to submit the form.
+- **`:optional` Pseudo-class**: This pseudo-class applies styles input elements that are not required and can be left empty.
+- **`:autofill` Pseudo-class**: This pseudo-class applies styles to input fields that the browser automatically fills with saved data.
+
+## Location Pseudo-classes
+
+- **Location Pseudo-classes**: These pseudo-classes are used for styling links and elements that are targeted within the current document.
+- **`:any-link` Pseudo-class**: This pseudo-class is a combination of the :link and :visited pseudo-classes. So, it matches any anchor element with an href attribute, regardless of whether it’s visited or not.
+- **`:link` Pseudo-class**: This pseudo-class allows you to target all unvisited links on a webpage. You can use it to style links differently before the user clicks on them.
+- **`:local-link` Pseudo-class**: This pseudo-class targets links that point to the same document. It can be useful when you want to differentiate internal links from external ones.
+- **`:visited` Pseudo-class**: This pseudo-class targets a link the user has visited. 
+- **`:target` Pseudo-class**: This pseudo-class is used to apply styles to an element that is the target of a URL fragment 
+
+## Tree-structural Pseudo-classes
+
+- **Tree-structural Pseudo-classes**: These pseudo-classes allow you to target and style elements based on their position within the document tree. 
+- **`:root` Pseudo-class**: This pseudo-class is usually the root `<html>` element. It helps you target the highest level in the document so you can apply a common style to the entire document.        
+- **`:empty` Pseudo-class**: Empty elements, that is, elements with no children other than white space, are also included in the document tree. That's why there's an `:empty` pseudo-class to target empty elements.
+- **`:nth-child(n)` Pseudo-class**: This pseudo-class allows you to select elements based on their position within a parent.
+- **`:nth-last-child(n)` Pseudo-class**: This pseudo-class enables you to select elements by counting from the end.
+- **`:first-child` Pseudo-class**: This pseudo-class selects the first element in a parent element or the document.
+- **`:last-child` Pseudo-class**: This pseudo-class selects the last element in a parent element or the document
+- **`:only-child` Pseudo-class**: This pseudo-class selects the only element in a parent element or the document
+- **`:first-of-type` Pseudo-class**: This pseudo-class selects the first occurrence of a specific element type within its parent.
+- **`:last-of-type` Pseudo-class**: This pseudo-class selects the last occurrence of a specific element type within its parent.
+- **`:nth-of-type(n)` Pseudo-class**: This pseudo-class allows you to select a specific element within its parent based on its position among siblings of the same type.
+- **`:only-of-type` Pseudo-class**: This pseudo-class selects an element if it's the only one of its type within its parent. 
+
+
+## Functional Pseudo-classes
+
+- **Functional Pseudo-classes**: Functional pseudo-classes allow you to select elements based on more complex conditions or relationships. Unlike regular pseudo-classes which target elements based on a state (for example, :hover, :focus), functional pseudo-classes accept arguments.
+- **`:is()` Pseudo-class**: This pseudo-class takes a list of selectors (ex. `ol`, `ul`) and selects an element that matches one of the selectors in the list.
+
+```html
+<p class="example">This text will change color.</p>
+<p>This text will not change color.</p>
+<p>This text will not change color.</p>
+<p class="this-works-too">This text will change color.</p>
+```
+
+```css
+p:is(.example, .this-works-too) {
+    color: red;
+}
+```
+
+- **`:where()` Pseudo-class**: This pseudo-class takes a list of selectors (ex. `ol`, `ul`) and selects an element that matches one of the selectors in the list. The difference between `:is` and `:where` is that the latter will have a specificity of 0.
+
+```css
+:where(h1, h2, h3) {
+    margin: 0;
+    padding: 0;
+}
+```
+
+- **`:has()` Pseudo-class**: This pseudo-class is often dubbed the `"parent"` selector because it allows you to style elements who contain child elements specified in the selector list.
+
+```css
+article:has(h2) {
+    border: 2px solid hotpink;
+}
+```
+
+## Pseudo-elements 
+
+- **`::before` Pseudo-element**: This pseudo-element uses the `content` property to insert cosmetic content like icons just before the element.
+- **`::after` Pseudo-element**: This pseudo-element uses the `content` property to insert cosmetic content like icons just after the element.
+- **`::first-letter` Pseudo-element**: This pseudo-element targets the first letter of an element's content, allowing you to style it.
+- **`::marker` Pseudo-element**: This pseudo-element lets you select the marker (bullet or numbering) of list items for styling.
 
 # --assignment--