Why is a div with "display: table-cell;" not affected by margin?

Question

Cause

From the MDN documentation:

[The margin property] applies to all elements except elements with table display types other than table-caption, table and inline-table

In other words, the margin property is not applicable to display:table-cell elements.

Solution

Consider using the border-spacing property instead.

Note it should be applied to a parent element with a display:table layout and border-collapse:separate.

For example:

HTML

<div class="table">
    <div class="row">
        <div class="cell">123</div>
        <div class="cell">456</div>
        <div class="cell">879</div>
    </div>
</div>

CSS

.table {display:table;border-collapse:separate;border-spacing:5px;}
.row {display:table-row;}
.cell {display:table-cell;padding:5px;border:1px solid black;}

See jsFiddle demo

---

Different margin horizontally and vertically

As mentioned by Diego Quirós, the border-spacing property also accepts two values to set a different margin for the horizontal and vertical axes.

For example

.table {/*...*/border-spacing:3px 5px;} /* 3px horizontally, 5px vertically */

You can use inner divs to set the margin.

<div style="display: table-cell;">
   <div style="margin:5px;background-color: red;">1</div>
</div>
<div style="display: table-cell; ">
  <div style="margin:5px;background-color: green;">1</div>
</div>

JS Fiddle

Table cells don't respect margin, but you could use transparent borders instead:

div {
  display: table-cell;
  border: 5px solid transparent;
}

Note: you can't use percentages here... :(

If you have div next each other like this

<div id="1" style="float:left; margin-right:5px">

</div>
<div id="2" style="float:left">

</div>

This should work!