Fix a couple of minor typos

Author: birtles

Overview.bs

@@ -1374,7 +1374,7 @@ time</a> of the animation's <a>target effect</a>.
 If the animation has no <a>target effect</a>, the <a>target effect
 end</a> is zero.
 
-An animation with a negative <a lt="animation playback rate">playback
+For an animation with a negative <a lt="animation playback rate">playback
 rate</a>, the <a>current time</a> continues to decrease until it
 reaches zero.
 
@@ -2706,7 +2706,7 @@ Note: While the time spaces themselves are not bounded, Web
 In addition to these time spaces we can also refer to the
 <em>document time space</em> which is time space of the <a>time
 values</a> of the <a>default document timeline</a> of the
-{{Document}} of the <a>current global object</a>
+{{Document}} of the <a>current global object</a>.
 
 </div>