How to float 3 divs side by side using CSS?

Question

Just give them a width and float: left;, here's an example:

<div style="width: 500px;">
 <div style="float: left; width: 200px;">Left Stuff</div>
 <div style="float: left; width: 100px;">Middle Stuff</div>
 <div style="float: left; width: 200px;">Right Stuff</div>
 <br style="clear: left;" />
</div>

The modern way is to use the CSS flexbox, see support tables.

.container {
  display: flex;
}
.container > div {
  flex: 1; /*grow*/
}

<div class="container">
  <div>Left div</div>
  <div>Middle div</div>  
  <div>Right div</div>
</div>

You can also use CSS grid, see support tables.

.container {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr; /* fraction*/
}

<div class="container">
  <div>Left div</div>
  <div>Middle div</div>  
  <div>Right div</div>
</div>

It is same way as you do for the two divs, just float the third one to left or right too.

<style>
  .left{float:left; width:33%;}
</style>

<div class="left">...</div>
<div class="left">...</div>
<div class="left">...</div>

float them all left

make sure a width is specified that they can all fit in their container (either another div or the window), otherwise they will wrap

<br style="clear: left;" />

that code that someone posted up there, it did the trick!!! when i paste it just before closing the Container DIV, it helps clear all subsequent DIVs from overlapping with the DIVs i've created side-by-side at the top!

<div>
<div class="left"></div>
<div class="left"></div>
...
...
<div class="left"></div>
<!--  then magic trick comes here  -->
<br style="clear: left;" />
</div>

tadaa!! :)