Fix typo

Author: Psychpsyo

css-style-attr-1/Overview.src.html

@@ -192,7 +192,7 @@ <h2 id="syntax">Syntax and Parsing</h2>
 
 <div class="note">
 <p>Although the grammar allows it,
-no at-rule valid in style attributes is define at the moment.
+at the moment no at-rule is defined to be valid in style attributes.
 The forward-compatible parsing rules are such that a declaration following an at-rule
 is not ignored:
 <pre>&lt;span style="@unsupported { splines: reticulating } color: green"></pre>