Pseudo elements (objects) Selector

Pseudo elements (objects) in front of the selector :( these pseudo-element selector colon can write a set, may be written two;)
        . 1), After ::: use with a content attribute, the content is defined in the object . (You must have an attribute content: "";)

    Syntax: Selector:: after {content: "Text";}
               selector:: after {content: url (image path);

         2), :: before: use with a content attribute, the content is defined in front of the object.

    Syntax: Selector:: before {content: "Text";}
               selector:: before {content: url (image path);
    

         3) the style of the first character in the :: first-letter-defined objects.
     Note: * (the dummy element for block-level element only)

         4) :: first-line: first line pattern within the definition of an object.
    Note: * (The pseudo-element can only be used for block-level element) 
   
  hidden attribute: visibility: visible display / hidden hide;

   visibility: hidden; and display: none; difference:
   visibility: hidden; property causes the object is not visible, but the object did not change in the space occupied by the Web page, a blank equal to stay out of the area;
   and display: none attribute causes this object does not display completely disappeared, and no longer occupy the position.
        
   Summary: visibility: hidden; let the elements hidden; position of the element is retained;
              Run the display: none: Let element hiding; position of the element is not retained, and are hidden