Say I have this html:
<div id="sidebar">
TestTestTestTestTestTest
</div>
<div id="content">
Content
</div>
And this CSS:
#sidebar {
float:left;
width:15%;
border:1px solid red;
}
#content {
float:left;
width:75%;
border:1px solid green;
}
As you can see here , the content on the sidebar is going under the content container. How can I avoid that so that it would break a line and continue in the sidebar?

You can not manage text if there are no white spaces.
You can avoid at this issue adding the ellipsis on the
#sidebar:http://jsfiddle.net/t4rNp/3/