Example h1 {font:1em Arial; color:#000;}

h1 – element selector
{font:1em Arial; color:#000;} – declaration block

property -> value
font -> 1em Arial

Element Selector(tag): h1
Class Selector: .author
ID Selector: #header
Descendent Selector:#mainContent h1
Pseudo-Class Selectors: :link | :visited | :hover |:active