Can I use different styles within one div - html

Question

I'm using a script to do a mouseover effect with images and also highlighting text in a different color using the getElementById phrase. I understand that an ID can only be used once, and if it needs to be used more than once I should use class. But there is no getElementByClass function. I have 2 areas of type that I want to highlight, one is centered, the other is left justified. Is there a way to use the same id for both styles?
<div id="georgia">
<style="text-align: center;">
<strong>Headquarters:
</strong>
</style>more text here
</div>
This is the script I am using:
<script type="text/javascript">// < ![CDATA[
function on(el) {
if (document.getElementById(el)) {
document.getElementById(el).style.color="green";
};
};
function off(el) {
if (document.getElementById(el)) {
document.getElementById(el).style.color="";
};
};
// ]]></script>
So what you are saying is I can replace the getElementById with getElementByClassName then it will work?
This is the format I'm using, the first part of the text (Headquarters) is not showing up, but the second part (more text here) is fine.

Answer 1

You need to use document.getElementsByClassName, which returns a list of the objects with that class name:
var all = document.getElementsByClassName("bar");
for(var i = 0; i < all.length; i++){
var obj = all[i];
obj.style.fontWeight = 'bold';
}
<div id="foo" class="bar">hi</div>
<div class="bar">bye</div>
<div id="bar">sup</div>