[css-nav-1] Modiy more precise description for setting search origin

Author: Jihye Hong

css-nav-1/Overview.bs

@@ -1089,19 +1089,17 @@ run the following steps:
     then return it.
 3. Otherwise, return <var>searchOrigin</var>.
 
-If the focus status changes not by the spatial navigation, the <var>searchOrigin</var> is set from the <var>old focus target</var> as following:
-1. If <var>old focus target</var> becomes out of the viewport by scrolling,
-    then let <var>searchOrigin</var> be the scroll container which triggers the scroll behavior.
-2. If <var>old focus target</var> becomes
+If the status of <var>old focus target</var> changed not by the spatial navigation,
+the <var>searchOrigin</var> is set from the <var>old focus target</var> as following:
+1. If <var>old focus target</var> becomes
     <a>actually disabled</a> or
     <a>expressly inert</a> or
     not <a>being rendered</a>,
     then let <var>searchOrigin</var> be the [=boundary box=] of <var>old focus target</var>.
-3. If <var>old focus target</var> is <a>removed</a>,
-    then let <var>searchOrigin</var> be the [=boundary box=] of <var>old focus target</var>.
-4. Otherwise,
-    let <var>searchOrigin</var> be the viewport of <var>old focus target</var>'s Document.
-
+2. If <var>old focus target</var> is <a>removed</a>,
+    then let <var>searchOrigin</var> be the [=boundary box=] of <var>old focus target</var> with the position of <var>old focus target</var> when it existed.
+3. Otherwise,
+    let <var>searchOrigin</var> be the viewport of <var>old focus target</var>'s <a>spatial navigation container</a>.
 </div>
 
 <div algorithm="to find focusable areas">