[css-animations-1] Tweak wording and formatting of 0s animation-duration description

Fixes w3c#4120.

Author: birtles

css-animations-1/Overview.bs

@@ -509,26 +509,27 @@ The 'animation-duration' property</h3>
 	Canonical order: per grammar
 	</pre>
 
-	<dl>
-		<dt><dfn value for=animation-duration><<time>></dfn>
-		<dd>
-			The <<time>> specifies the length of time that an animation takes to complete one cycle.
-			A negative <<time>> is invalid.
-
-			If the <<time>> is ''0s'', like the initial value,
-			the keyframes of the animation have no effect,
-			but the animation itself still occurs instantaneously.
-			Specifically, start and end events are fired; if
-			'animation-fill-mode' is set to ''backwards'' or
-			''both'', the first frame of the animation, as defined by
-			'animation-direction', will be displayed during the
-			'animation-delay'. Then the last frame of the animation,
-      as defined by 'animation-direction', will be displayed if
-      'animation-fill-mode' is set to ''forwards'' or ''both''.  If
-      'animation-fill-mode' is set to ''animation-fill-mode/none''
-			then the animation has no visible effect.
-		</dd>
-	</dl>
+<dl>
+<dt><dfn value for=animation-duration><<time>></dfn>
+<dd>
+The <<time>> specifies the length of time that an animation takes to complete one cycle.
+A negative <<time>> is invalid.
+
+If the <<time>> is ''0s'', like the initial value,
+the keyframes of the animation have no effect,
+but the animation itself still occurs instantaneously.
+Specifically, start and end events are fired;
+if 'animation-fill-mode' is set to ''backwards'' or ''both'',
+the first frame of the animation,
+as defined by 'animation-direction',
+will be displayed during the 'animation-delay'.
+After the 'animation-delay' the last frame of the animation,
+as defined by 'animation-direction',
+will be displayed if 'animation-fill-mode' is set to ''forwards'' or ''both''.
+If 'animation-fill-mode' is set to ''animation-fill-mode/none''
+the animation will have no visible effect.
+</dd>
+</dl>
 
 <h3 id="animation-timing-function">
 The 'animation-timing-function' property</h3>