Corrected capitalization, corrected to American spellings and typos (#30685)

* Translate challenge subtitles and example challenge text to Spanish

* Corrected errors in syntax and punctuation

* Multiple corrections of it/s to its plus other grammar corrections

* Correction and added paragraph to CSS Flex article

* Corrected my own typo

* Corrected capitalization, American spellings and typos

guide/english/html/elements/blockquote-tag/index.md

@@ -4,7 +4,7 @@ title: Blockquote Tag
 ## Blockquote Tag
 
 ### Purpose
-The HTML `<blockquote>` element breaks out a quote from the surrounding content. This allows the reader to clearly see the quotation as material attributed to it's original author. 
+The HTML `<blockquote>` element breaks out a quote from the surrounding content. This allows the reader to clearly see the quotation as material attributed to its original author. 
 
 ### Usage
 Just like the "H" tags send signals to a reader that the information is important, the blockquote alerts a reader that the information they're reading is from an outside source.  The `<blockquote>` tag can include A URL for the source of the quotation may be given using the cite attribute, while a text representation of the source can be given using the `<cite>` element.

guide/english/html/html5-semantic-elements/index.md

@@ -2,11 +2,11 @@
 title: HTML5 Semantic Elements
 ---
 ## HTML5 Semantic Elements
-Semantic HTML elements clearly describe it's meaning in a human and machine readable way. Elements such as `<header>`, `<footer>` and `<article>` are all considered semantic because they accurately describe the purpose of the element and the type of content that is inside them.
+Semantic HTML elements clearly describe its meaning in a human and machine readable way. Elements such as `<header>`, `<footer>` and `<article>` are all considered semantic because they accurately describe the purpose of the element and the type of content that is inside them.
 
 
 ### A Quick History
-HTML was originally created as a markup language to describe documents on the early internet. As the internet grew and was adopted by more people, it's needs changed. Where the internet was originally inteded for sharing scientific documents, now people wanted to share other things as well. Very quickly, people started wanting to make the web look nicer. Because the web was not initially built to be designed, programmers used different hacks to get things laid out in different ways. Rather than using the ```<table></table>``` to describe information using a table, programmers would use them to position other elements on a page. As the use of visually designed layouts progressed, programmers started to use a generic "non-semantic" tag like `<div>`. They would often give these elements a `class` or `id` attribute to describe their purpose. For example, instead of `<header>` this was often written as `<div class="header">`. As HTML5 is still relatively new, this use of non-semantic elements is still very common on websites today.
+HTML was originally created as a markup language to describe documents on the early internet. As the internet grew and was adopted by more people, its needs changed. Where the internet was originally inteded for sharing scientific documents, now people wanted to share other things as well. Very quickly, people started wanting to make the web look nicer. Because the web was not initially built to be designed, programmers used different hacks to get things laid out in different ways. Rather than using the ```<table></table>``` to describe information using a table, programmers would use them to position other elements on a page. As the use of visually designed layouts progressed, programmers started to use a generic "non-semantic" tag like `<div>`. They would often give these elements a `class` or `id` attribute to describe their purpose. For example, instead of `<header>` this was often written as `<div class="header">`. As HTML5 is still relatively new, this use of non-semantic elements is still very common on websites today.
 
 #### List of new semantic elements
 The semantic elements added in HTML5 are:

guide/english/html/tutorials/how-to-horizontally-center-a-div-tag-in-another-div-tag/index.md

@@ -27,7 +27,7 @@ There are a couple ways you can tacklet this, but for this tutorial let's focus
 
 
 ### Example of Centering a Div Tag with Margins
-If you specify a `width` on your child div you can use `margin: auto`. This will center your child `<div>` by evenly distributing it's left-and-right margins.
+If you specify a `width` on your child div you can use `margin: auto`. This will center your child `<div>` by evenly distributing its left-and-right margins.
 
 ```css
 .parent {