Update CSS for clarity.

- More relevant introduction
- More consistent and clear wording
- More consistent formatting

css.html.markdown

@@ -6,20 +6,21 @@ contributors:
     - ["Geoffrey Liu", "https://github.com/g-liu"]
     - ["Connor Shea", "https://github.com/connorshea"]
     - ["Deepanshu Utkarsh", "https://github.com/duci9y"]
+    - ["Tyler Mumford", "https://tylermumford.com"]
 filename: learncss.css
 ---
 
-In the early days of the web there were no visual elements, just pure text. But with further development of web browsers, fully visual web pages also became common.
+Web pages are built with HTML, which specifies the content of a page. CSS (Cascading Style Sheets) is a separate language which specifies a page's **appearance**.
 
-CSS helps maintain separation between the content (HTML) and the look-and-feel of a web page.
+CSS code is made of static *rules*. Each rule takes one or more *selectors* and gives specific *values* to a number of visual *properties*. Those properties are then applied to the page elements indicated by the selectors.
 
-CSS lets you target different elements on an HTML page and assign different visual properties to them.
+This guide has been written with CSS 2 in mind, which is extended by the new features of CSS 3.
 
-This guide has been written for CSS 2, though CSS 3 is fast becoming popular.
-
-**NOTE:** Because CSS produces visual results, in order to learn it, you need try everything in a CSS playground like [dabblet](http://dabblet.com/).
+**NOTE:** Because CSS produces visual results, in order to learn it, you need to try everything in a CSS playground like [dabblet](http://dabblet.com/).
 The main focus of this article is on the syntax and some general tips.
 
+## Syntax
+
 ```css
 /* comments appear inside slash-asterisk, just like this line!
    there are no "one-line comments"; this is the only comment style */
@@ -28,7 +29,7 @@ The main focus of this article is on the syntax and some general tips.
    ## SELECTORS
    #################### */
 
-/* the selector is used to target an element on a page.
+/* the selector is used to target an element on a page. */
 selector { property: value; /* more properties...*/ }
 
 /*
@@ -69,7 +70,7 @@ div { }
 [otherAttr|='en'] { font-size:smaller; }
 
 
-/* You can concatenate different selectors to create a narrower selector. Don't
+/* You can combine different selectors to create a more focused selector. Don't
    put spaces between them. */
 div.some-class[attr$='ue'] { }
 
@@ -92,7 +93,7 @@ div.some-parent.class-name { }
 .i-am-any-element-before ~ .this-element { }
 
 /* There are some selectors called pseudo classes that can be used to select an
-   element when it is in a particular state */
+   element only when it is in a particular state */
 
 /* for example, when the cursor hovers over an element */
 selector:hover { }
@@ -103,7 +104,7 @@ selector:visited { }
 /* or hasn't been visited */
 selected:link { }
 
-/* or an element in focus */
+/* or an element is in focus */
 selected:focus { }
 
 /* any element that is the first child of its parent */
@@ -156,10 +157,10 @@ selector {
     color: tomato;               /* a named color */
     color: rgb(255, 255, 255);   /* as rgb values */
     color: rgb(10%, 20%, 50%);   /* as rgb percentages */
-    color: rgba(255, 0, 0, 0.3); /* as rgba values (CSS 3) Note: 0 < a < 1 */
+    color: rgba(255, 0, 0, 0.3); /* as rgba values (CSS 3) Note: 0 <= a <= 1 */
     color: transparent;          /* equivalent to setting the alpha to 0 */
     color: hsl(0, 100%, 50%);    /* as hsl percentages (CSS 3) */
-    color: hsla(0, 100%, 50%, 0.3); /* as hsla percentages with alpha */
+    color: hsla(0, 100%, 50%, 0.3); /* as hsl percentages with alpha */
     
     /* Images as backgrounds of elements */
     background-image: url(/img-path/img.jpg); /* quotes inside url() optional */
@@ -194,7 +195,7 @@ Save a CSS stylesheet with the extension `.css`.
 
 ## Precedence or Cascade
 
-An element may be targeted by multiple selectors and may have a property set on it in more than once. In these cases, one of the rules takes precedence over others. Generally, a rule in a more specific selector take precedence over a less specific one, and a rule occuring later in the stylesheet overwrites a previous one.
+An element may be targeted by multiple selectors and may have a property set on it in more than once. In these cases, one of the rules takes precedence over others. Rules with a more specific selector take precedence over a less specific one, and a rule occuring later in the stylesheet overwrites a previous one.
 
 This process is called cascading, hence the name Cascading Style Sheets.
 
@@ -238,10 +239,10 @@ Most of the features in CSS 2 (and many in CSS 3) are available across all brows
 
 ## Resources
 
-* To run a quick compatibility check, [CanIUse](http://caniuse.com).
-* CSS Playground [Dabblet](http://dabblet.com/).
-* [Mozilla Developer Network's CSS documentation](https://developer.mozilla.org/en-US/docs/Web/CSS)
-* [Codrops' CSS Reference](http://tympanus.net/codrops/css_reference/)
+* [CanIUse](http://caniuse.com) (Detailed compatibility info)
+* [Dabblet](http://dabblet.com/) (CSS playground)
+* [Mozilla Developer Network's CSS documentation](https://developer.mozilla.org/en-US/docs/Web/CSS) (Tutorials and reference)
+* [Codrops' CSS Reference](http://tympanus.net/codrops/css_reference/) (Reference)
 
 ## Further Reading