fix(proton): light color scheme for message iframe (catppuccin#919)

Author: Lichthagel

styles/proton/catppuccin.user.css

@@ -2,7 +2,7 @@
 @name Proton Catppuccin
 @namespace github.com/catppuccin/userstyles/styles/proton
 @homepageURL https://github.com/catppuccin/userstyles/tree/main/styles/proton
-@version 0.1.6
+@version 0.1.7
 @updateURL https://github.com/catppuccin/userstyles/raw/main/styles/proton/catppuccin.user.css
 @supportURL https://github.com/catppuccin/userstyles/issues?q=is%3Aopen+is%3Aissue+label%3Aproton
 @description Soothing pastel theme for Proton
@@ -236,6 +236,10 @@
       background-color: var(--navigation-current-item-background-color);
       color: var(--email-item-unread-text-color);
     }
+
+    .message-content:not(.plain) .message-iframe iframe {
+      color-scheme: light;
+    }
   }
 }