[css-env-1] Spec safe-area-max-inset-* envvars (#11617)

* [css-env-1] Spec safe-area-max-inset-* envvars

* Rename max safe area insets to safe area max insets

* Add link to viewport size and large viewport size

css-env-1/Overview.bs

@@ -126,6 +126,42 @@ safe area rectangle.
 
 <index type=value for=env()></index>
 
+Safe area maximum inset variables {#safe-area-max-insets}
+------------------------------------------------------------------
+
+<table dfn-type=value dfn-for="env()">
+	<tr>
+		<th>Name
+		<th>Value
+		<th>Number of dimensions
+	<tr>
+		<td><dfn>safe-area-max-inset-top</dfn>
+		<td><<length>>
+		<td>0 (scalar)
+	<tr>
+		<td><dfn>safe-area-max-inset-right</dfn>
+		<td><<length>>
+		<td>0 (scalar)
+	<tr>
+		<td><dfn>safe-area-max-inset-bottom</dfn>
+		<td><<length>>
+		<td>0 (scalar)
+	<tr>
+		<td><dfn>safe-area-max-inset-left</dfn>
+		<td><<length>>
+		<td>0 (scalar)
+</table>
+
+The safe area maximum insets are four [=environment variables=]
+that are tied to the <a href="#safe-area-insets">safe area inset variables</a>.
+Unlike the safe area inset variables which are dynamic values,
+the safe area maximum insets are static values
+that represent the maximum value of their dynamic counterpart
+when dynamic UA interfaces are retracted,
+making the [=layout viewport=] size the [=large viewport size=].
+
+<index type=value for=env()></index>
+
 Viewport segment variables {#viewport-segments}
 ------------------------------------------------------------------