'.' selector
'.' selector is a class level selector. The dot operator is used to create a style class which can then be applied on multiple html elements.
'#' selector
'#' selector is an element level selector. Hash operator is used to applying style on a particular element whose id is the same as used in '#' selector
Example
Following the example, shows usage of '.' as well as '#' selector on three div elements.
<!DOCTYPE html> <html> <head> <title>Selector Example>/title> <style> .blackBorder { border: 2px solid black; } #redDiv { border: 2px solid red; } </style> </head> <body> <div> No Border Box </div> <div class="blackBorder"> Black Border Box </div> <div id="redDiv"> Red Border Box </div> <div> No Border Box </div> <div class="blackBorder"> Black Border Box </div> </body> </html>