Move definition of Visual Viewport from CSSOM-View

Signed-off-by: Shubham Gupta <shubham.gupta@chromium.org>

Author: shubhamg13

css-viewport-1/Overview.bs

@@ -91,24 +91,35 @@ For [=paged media=], the initial containing block is based on the page area.
 The page area can be set through ''@page'' rules.
 
 This specification introduces a way of overriding the size of the viewport
-provided by the user agent (UA). Because of this, we need to introduce the
-difference between the [=initial viewport=] and the [=layout viewport=].
+provided by the user agent (UA). Because of this, we need to define [=initial viewport=], [=layout viewport=] and [=visual viewport=].
 
 <dl>
 	<dt><dfn>initial viewport</dfn></dt>
 	<dd>
 		This refers to the viewport before any UA or author styles have
 		overridden the viewport given by the window or viewing area of the UA.
-		Note that the [=initial viewport=] size will change with the
+		
+		Note: The [=initial viewport=] size will change with the
 		size of the window or viewing area.</dd>
 	<dt><dfn>layout viewport</dfn></dt>
 	<dd>
 		This is the viewport you get after processing the viewport
 		<code>&lt;meta&gt;</code> tag.
 	</dd>
+	<dt><dfn>visual viewport</dfn></dt>
+	<dd>
+		The portion of the layout viewport that is currently visible. 
+		This is the result of applying scale transform to its layout viewport.
+		This transform is applied to the <a>canvas</a> of the <a>layout viewport</a> and does not affect its internal coordinate space.
+		The magnitude of the scale transform is known as the <a>visual viewport</a>'s scale factor.
+		
+		Note: The [=visual viewport=] can be smaller than the [=layout viewport=]. 
+	</dd>
 </dl>
 
-ISSUE: Define visual viewport.
+Note: The scale transform of the [=visual viewport=]
+is often referred to as "pinch-zoom". Conceptually, this transform changes the size of the CSS <a>reference pixel</a> and changes the size
+of the layout viewport (inversally) proportionally so that it does not cause reflow of the page's contents.
 
 When the [=layout viewport=] cannot fit inside the window or
 viewing area, either because the [=layout viewport=] is

cssom-view-1/Overview.bs

@@ -293,17 +293,9 @@ The <dfn>ending edges</dfn> of a particular set of edges of a box or element are
  <dd>The top and right edges.
 </dl>
 
-The <dfn>visual viewport</dfn> is a kind of <a>viewport</a> whose <a>scrolling area</a> is another <a>viewport</a>,
-called the <dfn export>layout viewport</dfn>.
-
-In addition to scrolling, the <a>visual viewport</a> may also apply a scale transform to its <a>layout viewport</a>.
-This transform is applied to the <a>canvas</a> of the <a>layout viewport</a> and does not affect its internal coordinate space.
-
-Note: The scale transform of the visual viewport is often referred to as "pinch-zoom". Conceptually, this transform
-changes the size of the CSS <a>reference pixel</a> but changes the size of the layout viewport proportionally so that it
-does not cause reflow of the page's contents.
-
-The magnitude of the scale transform is known as the <a>visual viewport</a>'s <dfn>scale factor</dfn>.
+The <a href="https://drafts.csswg.org/css-viewport-1/Overview.html#visual-viewport">visual viewport</a>'s <a>scrolling area</a> is another
+<a href="https://www.w3.org/TR/CSS2/visuren.html#viewport">viewport</a>,
+the <a href="https://drafts.csswg.org/css-viewport-1/Overview.html#layout-viewport">layout viewport</a>.
 
 <style>
       @keyframes lvmove {