margin-top of div doubles if adjacent parent div has no border

Hi,

I use several (in my example 2) div boxes with absolute width (200) on the left and a box with variable width (remaining space) on the right.
The boxes on the left are included in a container (divleft), the box on the right is included in divright.

In my example, the right container has a red border.
If I remove this border (i.e. change 1px to 0px), then "BOX1" has double its distance to the top of the page - which is 20 pixels (while "BOX RIGHT" is still 10 pixels from the top). If I change the margin of the class "box" from 10px to 5 px, then only "BOX RIGHT" is 5 pixels from the top, while "BOX1" is 10 pixels from the top.

Can somebody please explain this behavior to me?

<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>TEST</title>
<meta http-equiv="Content-Type" content="text/html; charset=utf-8">
<meta http-equiv="pragma" content="no-cache">
<meta http-equiv="expires" content="0">
<style type="text/css">

* { margin:0px; padding:0px; }

#divleft { float:left; width:200px; border:0px solid red; } /* left container */
#divright { margin-left:200px; border:1px solid red; } /* right container */

.box { border-style:solid; border-color:gray; border-width:1px; margin:10px; padding:5px; } /* This margin is not always 10px */
.boxtitle { background-color:gray; color:white; font-weight:bold; margin:0px; padding:5px; }

</style>
</head>
<body>

<div id="divleft"> <!-- left container -->

<div class="box boxleft"> <!-- BOX1 -->
<p class="boxtitle">BOX1</p>

---<br>

</div>



<div class="box boxleft"> <!-- BOX2 -->
<p class="boxtitle">BOX2</p>

---<br>

</div>

</div>

<div id="divright"> <!-- right container -->

<div class="box boxright"> <!-- BOX RIGHT -->
<p class="boxtitle">BOX RIGHT</p>


TESTMAIN!
<br>

</div>


</div>

</body>
</html>


<!DOCTYPE HTML PUBLIC "-//W3C//DTD HTML 4.01//EN"
"http://www.w3.org/TR/html4/strict.dtd">
<html>
<head>
<title>TEST</title>
<style type="text/css">
* { margin: 0; padding: 0; }
#container {
  padding-top: 1px;
}
#divleft { 
  float:left;
  width:200px;
} /* left container */
#divright {
  margin: 0 0 0 200px;
  border: 0px solid red;
} /* right container */
.box {
  border: 1px solid gray;
  margin: 5px;
} /* This margin is not always 10px */
</style>
</head>
<body>
<div id="container">
<div id="divleft">
  <div class="box boxleft">
    ---
  </div>
</div>
<div id="divright">
  <div class="box boxright">
    TESTMAIN!
  </div>
</div>
</div>
</body>
</html>

margin-top of div doubles if adjacent parent div has no border

basic6

Shado

basic6

Fotiman

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