Fix Caps-lock-is-on color in light theme #4320

When a Polkit dialog is open to ask for the password, if the
user activates the Caps Lock, a message appears under the text
entry notifying that it is active, to warn the user.

In dark theme, this message is painted in yellow, which is fine
because it gives a good contrast against the background; but in
ligth theme, a slightly darker yellow is used, which has poor
contrast. This goes against the accessibility (A11Y)
requirements of having, at least, a 4.5/1 contrast ratio in text.
This only happens in Yaru, because in upstream Gnome theme, the
dialog is always dark, no matter what style (dark or light) is
selected by the user.

This patch fixes this by setting the WARNING text color to black
in light themes.

Author: sergio-costas

gnome-shell/src/gnome-shell-sass/_default-colors.scss

@@ -17,7 +17,7 @@ $success_bg_color: if($variant == 'light', $green_4, $green_5);
 $success_fg_color: $light_1;
 $success_color: $success_bg_color;
 
-$warning_bg_color: if($variant == 'light', black, #cd9309); // uses darker off-palette yellow
+$warning_bg_color: if($variant == 'light', $yellow_5, #cd9309); // uses darker off-palette yellow
 $warning_fg_color: transparentize(black, .2);
 $warning_color: $warning_bg_color;
 

gnome-shell/upstream/theme/gnome-shell-sass/_default-colors.scss

@@ -17,9 +17,9 @@ $success_bg_color: if($variant == 'light', $green_4, $green_5);
 $success_fg_color: $light_1;
 $success_color: $success_bg_color;
 
-$warning_bg_color: if($variant == 'light', black, #cd9309); // uses darker off-palette yellow
+$warning_bg_color: if($variant == 'light', $yellow_5, #cd9309); // uses darker off-palette yellow
 $warning_fg_color: transparentize(black, .2);
-$warning_color: $warning_bg_color;
+$warning_color: if($variant == 'light', black, $warning_bg_color);
 
 $error_bg_color: if($variant == 'light', $red_3, $red_4);
 $error_fg_color: $light_1;