How Hexadecimal Works

• The Hexadecimal Numeral System
• Hex to RGB Convertor

References

• Named Colors and Hex Equivalents
• CSS Shorthand Properties
• CSS Shorthand Hexadecimal form

CSS Shadow generator

www.cssmatic.com/box-shadow 

The box-shadow property is relatively new to the world of CSS. You can use it to add a shadow to an element. If you want to try experimenting with box-shadows, check out this box-shadow generator from CSSmatic.

CSS Comments

The example for CSS comments:

p {
    color: blue;
}        
/* add CSS here */
h1 {
    color: red;
}