How to apply CSS style to all elements with same ID using one button?

Question

My idea was to create a button to hide/show all hidden text (Hide by highlighting the text in black, show by making the background color of the text transparent). But the codes,

Answer 1

I oppose the Same ID concept... But Try like below will be a answer to your question....

Fiddle Example : http://jsfiddle.net/RYh7U/65/

CSS

.mask
{
color : red;
}

Javascript :

function change()
{
 var elements = document.getElementById("p2").parentNode.getElementsByTagName("span");
    for(var i=0; i