CSS rule ".drop.a" applies to the "drag a" class

Question

I have the following HTML markup:

<div class="drag a"></div>
<div class="drop a"></div>

I also have the following CSS rule, which should only apply to my 2nd div:

.drop.a
{
   background-color:red;
}

This works fine except Internet Explorer 9, the CSS rule applies to both elements.

Why is this? I thought such CSS was universally compatible with all browsers?

Answer 1

I thought this type of CSS is universal for all browsers?

. IE 6 , . IE9 quirks, , .drop.a .a.

doctype , . , , - .