How come these DIVs will not display on the same line?

I have the following HTML:

<div id="root">
    <div id="left_side">LEFT</div>
    <div id="center_s">CENTER</div&开发者_开发知识库gt;
    <div id="right_side">RIGHT</div>
</div>

...and CSS:

#root {
    background-color: #eee;
}

#left_side {
    float: left;
}

#center_s {
    margin-left: auto;
    margin-right: auto;
    width: 65px;
    background-color: #ccc;
}

#right_side {
    float: right;
}

However, I get the following:

The DIV on the right is on a separate line, which is not what I want. How can I make it stay on the same line as the other DIVs?

Note: you can see a live demo and play around with the code here: http://jsfiddle.net/UDb4D/

It's because your #center_s div expands to the width of the remaining line. If you put #right_side above #center_s in the HTML order, it'll work fine.

See here:

http://jsfiddle.net/UDb4D/2/

Because the center has no float and right-floated elements need to appear first. Add float: left; to your #center_s or move the #right_side div before so it looks like this:

#root {
    background-color: #eee;
}

#left_side {
    float: left;
}

#center_s {
    margin-left: auto;
    margin-right: auto;
    width: 65px;
    background-color: #ccc;
    float: left;
}

#right_side {
    float: right;
}

<div id="root">
    <div id="right_side">RIGHT</div>
    <div id="left_side">LEFT</div>
    <div id="center_s">CENTER</div>    
</div>

I quickly hacked this up. Bare in mind that I'm a developer, not a web designer.

<div id="root" align="center">
    <div id="right_side">RIGHT</div>
    <div id="center_s">CENTER</div>
    <div id="left_side">LEFT</div>
</div>

And...

#root {
    background-color: #eee;
}

#left_side {
    display: inline;
    float: left;
}

#center_s {
    display: inline;
    margin-left: auto;
    margin-right: auto;
    width: 65px;
    background-color: #ccc;
}

#right_side {
    display: inline;
    float: right;
}