CSS - selector rules on W3.org

https://www.w3.org/TR/CSS21/selector.html%23id-selectors

CSS - Creating High Resolution Background Images with CSS

http://www.sitepoint.com/watch-creating-high-resolution-background-images-with-css/

CSS - best place to choose right color palette for your web app

Here you will find variety of web sites samples of different color palette
http://www.colourlovers.com/

CSS - sample demo and github code of site with user image in circle

https://github.com/kimlabs/gentelella

CSS - how to live edit CSS in Chrome devTool

https://developer.chrome.com/devtools/docs/css-preprocessors

CSS - jsfiddle example of table row hover

http://jsfiddle.net/thirtydot/Pe6Xe/1/

TOOLS - Colorzilla, nice color picker tool for browser

Colorzilla - http://www.colorzilla.com/
Very nice plugin for browsers Chrome and Firefox. It allows to pick colors and see its numeric value in very handily way.

CSS - CSS3 tricks

http://habrahabr.ru/post/265451/
http://fox-hover.co.uk/basic-hover-pack/

SASS - bower install (link)

http://nano.sapegin.ru/all/bower

SASS - Resources about Sass maven plugin

http://www.yegor256.com/2014/06/26/sass-in-java-webapp.html

http://mvnrepository.com/artifact/org.jasig.maven/sass-maven-plugin/1.1.1

<dependency>
    <groupId>org.jasig.maven</groupId>
    <artifactId>sass-maven-plugin</artifactId>
    <version>1.1.1</version>
</dependency>

Font Awesome resources

http://www.bootstrapcdn.com/

CSS - left shadow line for any container

-webkit-box-shadow: -1px 0px 1px 0px rgba(0, 0, 0, 0.2);
-moz-box-shadow: -1px 0px 1px 0px rgba(0, 0, 0, 0.2);
box-shadow: -1px 0px 1px 0px rgba(0, 0, 0, 0.2);

HTML & CSS - Схлопывание внешних отступов

http://habrahabr.ru/post/257327/

Try your code online HTML + CSS (link)

http://jsfiddle.net/itamark/uAKNx/