CSS autofill - improve grammar in introduction (mdn#2403)

files/en-us/web/css/_colon_autofill/index.html

@@ -9,7 +9,7 @@
 ---
 <div>{{CSSRef}}</div>
 
-<p>The <strong><code>:autofill</code></strong> CSS <a href="/en-US/docs/Web/CSS/Pseudo-classes">pseudo-class</a> matches when an {{HTMLElement("input")}} element has its value autofilled by the browser. The class must stop matching if the user edits the field.</p>
+<p>The <strong><code>:autofill</code></strong> CSS <a href="/en-US/docs/Web/CSS/Pseudo-classes">pseudo-class</a> matches when an {{HTMLElement("input")}} element has its value autofilled by the browser. The class stops matching if the user edits the field.</p>
 
 <div class="notecard note"><p><strong>Note:</strong> The user agent style sheets of many browsers use <code>!important</code> in their <code>:-webkit-autofill</code> style declarations, making them non-overrideable by webpages without resorting to JavaScript hacks. For example Chrome has the following in its internal stylesheet:</p>
 <pre class="brush:css">background-color: rgb(232, 240, 254) !important;