Apply style ONLY on IE

Here is my block of CSS:

.actual-form table {
  padding: 5px 0 15px 15px;
  margin: 0 0 30px 0;
  display: block;
  width: 100%;
  background: #f9f9f9;
  border-top: 1px solid #d0d0d0;
  border-bottom: 1px solid #d0d0d0;
}

I only want IE 7, 8, and 9 to "see" width: 100%

What is the simplest way to accomplish this?

@media screen and (-ms-high-contrast: active), (-ms-high-contrast: none) {
   #myElement {
        /* Enter your style code */
   }
}

Explanation: It is a Microsoft-specific media query. Using -ms-high-contrast property specific to Microsoft IE, it will only be parsed in Internet Explorer 10 or greater. I have used both the valid values of the media query, so it will be parsed by IE only, whether the user has high contrast enabled or not.

Update 2017

Depending on the environment, conditional comments have been officially deprecated and removed in IE10+.

Original

The simplest way is probably to use an Internet Explorer conditional comment in your HTML:

<!--[if IE]>
<style>
    .actual-form table {
         width: 100%;
    }
</style>
<![endif]-->

There are numerous hacks (e.g. the underscore hack) you can use that will allow you to target only IE within your stylesheet, but it gets very messy if you want to target all versions of IE on all platforms.