[css-values] Add back note that was dropped when <resolution> was copied over from css-images.

Author: fantasai

css-values-3/Overview.bs

@@ -1338,6 +1338,11 @@ Resolution Units: the <<resolution>> type and ''&lt;resolution&gt;/dpi'', ''&lt;
 	All <<resolution>> units are <a>compatible</a>,
 	and ''&lt;resolution&gt;/dppx'' is their <a>canonical unit</a>.
 
+	<p class="note">Note that due to the 1:96 fixed ratio of CSS ''in'' to CSS ''px'',
+	''1dppx'' is equivalent to ''96dpi''.
+	This corresponds to the default resolution of images displayed in CSS:
+	see 'image-resolution'.
+
 	<div class="example">
 		The following @media rule uses Media Queries [[MEDIAQ]]
 		to assign some special style rules to devices that use two or more device pixels per CSS ''px'' unit:

css-values/Overview.bs

@@ -1425,6 +1425,11 @@ Resolution Units: the <<resolution>> type and ''&lt;resolution&gt;/dpi'', ''&lt;
 	All <<resolution>> units are <a>compatible</a>,
 	and ''&lt;resolution&gt;/x'' is their <a>canonical unit</a>.
 
+	<p class="note">Note that due to the 1:96 fixed ratio of CSS ''in'' to CSS ''px'',
+	''1dppx'' is equivalent to ''96dpi''.
+	This corresponds to the default resolution of images displayed in CSS:
+	see 'image-resolution'.
+
 	<div class="example">
 		The following @media rule uses Media Queries [[MEDIAQ]]
 		to assign some special style rules to devices that use two or more device pixels per CSS ''px'' unit: