Delete white space between divs

You get whitespace there because you have whitespace inbetween the divs. Whitespace between inline elements is interpreted as a space.

You have:

<div id="left_side">
    <div id="plan">
        <h1>div 1</h1>
    </div>
</div>
<div id="right_side">
    <div id="news">
        <h1>div 2</h1>
    </div>
</div>

Change for:

<div id="left_side">
    <div id="plan">
        <h1>div 1</h1>
    </div>
</div><div id="right_side">
    <div id="news">
        <h1>div 2</h1>
    </div>
</div>

However, this is a bad way to do what you want to do.

You should float the elements if thats what you want to do.