Question

For some reason I can’t align my divs next to each other. “Right” goes under “left”
What is wrong with my code?

HTML:

<div id="activity-container">
    <div id="activity-left">left</div>
    <div id="activity-right">right</div>
</div>

CSS:

#activity-container
{
    width:90%;
    background-color:#FFFF00;
    Height:400px;
    margin-left: auto;
    margin-right: auto;
}

#activity-left {
    border: 1px solid black; 
    color:#000;
    margin: 0 auto; 
    width: 20%; 
    float: left;
    position: relative; 
}

#activity-right {
    border: 1px solid black; 
    margin: 0 auto; 
    color:#000;
    width: 80%; 
    float: left;
    position: relative; 
}

Live demo: Tinkerbin

Answer 1

Your borders on the div-s adding 2px to their width. Remove them and they will be next to each other – jsFiddle

If you really need the borders, then mimic them with outline – jsFiddle

#activity-left {
    outline: 1px solid #000;
    color:#000;
    margin: 0 auto; 
    width: 20%; 
    float: left;
    position: relative; 
}

#activity-right {
    outline: 1px solid #000;
    margin: 0 auto; 
    color:#000;
    width: 80%; 
    float: left;
    position: relative; 
}​