Two divs side by side - Fluid display

Try a system like this instead:

.container {
  width: 80%;
  height: 200px;
  background: aqua;
  margin: auto;
  padding: 10px;
}

.one {
  width: 15%;
  height: 200px;
  background: red;
  float: left;
}

.two {
  margin-left: 15%;
  height: 200px;
  background: black;
}

<section class="container">
  <div class="one"></div>
  <div class="two"></div>
</section>

You only need to float one div if you use margin-left on the other equal to the first div's width. This will work no matter what the zoom and will not have sub-pixel problems.

Here's my answer for those that are Googling:

CSS:

.column {
    float: left;
    width: 50%;
}

/* Clear floats after the columns */
.container:after {
    content: "";
    display: table;
    clear: both;
}

Here's the HTML:

<div class="container">
    <div class="column"></div>
    <div class="column"></div>
</div>

Using this CSS for my current site. It works perfect!

#sides{
margin:0;
}
#left{
float:left;
width:75%;
overflow:hidden;
}
#right{
float:left;
width:25%;
overflow:hidden;
} 

This is easy with a flexbox:

#wrapper {
  display: flex;
}

#left {
  flex: 0 0 65%;
}

#right {
  flex: 1;
}

<div id="wrapper">
  <div id="left">Left side div</div>
  <div id="right">Right side div</div>
</div>