Chrome developer tools Style tab showing faded CSS definition, why?

I've been using Chrome for a long time now and I've never (well not that I can recall) come across CSS definitions in the Style panel that are faded. The selector hasn't been defined else where.

Example:

(Edit: Just to be clear, I'm not referring to the user agent stylesheet)

I can't figure out why it is faded and what this means. The definition appears to be editable but any changes to the values do not persist (i.e. as soon as I click off, it reverts back to original value) and has no effect on the web page.

I couldn't find any reference to this in the documentation for the tool. Can any of you kind folk shed any light on this?

The "faded" styles are ones that are not applied to the selected tag. So in your screenshot, you have an h1 rule which is normal colored -- that one is applied to whatever element you have selected -- and you have an .SubHeader h1 rule that is not being applied to the selected element.

You'll sometimes see this if you dynamically add a CSS rule (the + button in the chrome dev tools) but modify the selector so it doesn't apply to whichever element you have selected.

Rules that are faded are not applied to the element.

Take a look at this example

<!-- HTML -->
<div>
  <span>Test</span>
</div>

/* CSS */
div {
  color: #F0F;
  margin: 15px;
  stroke: #FFF;
  float: left;
}

If you open dev tools, you will notice that margin and float are faded, color and stroke are not. That is because span element inherited style rules from its parent, but only color and stroke rules are inheritable.

It means that the rule has been inherited:

http://code.google.com/chrome/devtools/docs/elements-styles.html#computed_style