Issue 3158 - Add CSS and HTML rules to coding style page

pages/coding-style.html

Index: pages/coding-style.html
===================================================================
--- a/pages/coding-style.html
+++ b/pages/coding-style.html
@@ -30,6 +30,18 @@
 <li>{{s18 In classes, prefix private functions with a single underscore to make them pseudo-private.}}</li>
 </ul>
 
+<h2 id="html-css">{{html-css HTML and CSS}}</h2>
+<ul>
+<li>{{html-css1 Follow the <a href="https://google.github.io/styleguide/htmlcssguide.xml">Google HTML/CSS Style Guide</a>.}}</li>

[Thomas Greiner, 2015/11/10 09:51:00]

Please use descriptive identifiers instead of numbers that seem dependent on the
order of the items (e.g. `html-css-general`).

[Thomas Greiner, 2015/11/10 09:51:00]

Don't forget about indentation. The Objective-C list shows how it should be.

The reason why the other lists are not properly indented is because those were
created in Anwiki.

[saroyanm, 2015/11/10 10:20:07]

Done.

[saroyanm, 2015/11/10 10:20:07]

Done, also added indentation to other elements.

+<li>{{html-css2 Use double over single quotation marks.}}</li>
+<li>{{html-css3 Don't omit optional HTML tags.}}</li>
+<li>{{html-css4 CSS color values should be specified in hexadecimal where possible.}}</li>
+<li>{{html-css5 CSS shorthand properties usage is optional.}}</li>
+<li>{{html-css6 CSS rule declaration order should follow the <a href="https://make.wordpress.org/core/handbook/best-practices/coding-standards/css/#property-ordering">WordPress CSS Coding Standards</a>.}}</li>
+<li>{{html-css7 CSS number values should specify units where possible.}}</li>
+<li>{{html-css8 CSS number values between -1 and 1 should specify a leading 0.}}</li>
+</ul>
+
 <h2 id="python">{{s19 Python}}</h2>
 <ul>
 <li>{{s20 Follow the Mozilla Coding Style's <a href="https://developer.mozilla.org/en-US/docs/Developer_Guide/Coding_Style#Python_Practices">Python practices</a>.}}</li>