[gtk/4.0-backports: 35/53] docs: Mention css drop-shadow filter

[Matthias Clasen <matthiasc src gnome org>]

commit e99fa00c8061763f084676caa42f94cbdf91df00
Author: Matthias Clasen <mclasen redhat com>
Date:   Wed Feb 3 20:27:55 2021 -0500

    docs: Mention css drop-shadow filter
    
    We don't support this filter, currently.

 docs/reference/gtk/css-properties.md | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)
---
diff --git a/docs/reference/gtk/css-properties.md b/docs/reference/gtk/css-properties.md
index ee55d14bf6..1cdcfa1acc 100644
--- a/docs/reference/gtk/css-properties.md
+++ b/docs/reference/gtk/css-properties.md
@@ -129,7 +129,7 @@ done with
 |:-----------|:----------|:------|
 |color       | [CSS Color Level 3](https://www.w3.org/TR/css3-color/#foreground) | |
 |opacity     | [CSS Color Level 3](https://www.w3.org/TR/css3-color/#opacity) | |
-|filter      | [CSS Filter Effect Level 1](https://drafts.fxtf.org/filters/#FilterProperty) | |
+|filter      | [CSS Filter Effect Level 1](https://drafts.fxtf.org/filters/#FilterProperty) | CSS allows 
drop-shadow |
 |font-family | [CSS Fonts Level 3](https://www.w3.org/TR/css3-fonts/#font-family-prop) | defaults to 
gtk-font-name setting |
 |font-size   | [CSS Fonts Level 3](https://www.w3.org/TR/css3-fonts/#font-size-prop) | defaults to 
gtk-font-name setting |
 |font-style  | [CSS Fonts Level 3](https://www.w3.org/TR/css3-fonts/#font-style-prop) | |