Remove distinct --xh-popup-bg color

+ Controls background on popup alerts and dialogs - was a somewhat distracting one-off color, noticeable in eg App Options dialog, where it reduced legibility of the contents for apps with a complex set of options controls.
+ Reset to match the primary `--xh-bg` color by default - apps can customize if they need.

CHANGELOG.md

@@ -25,6 +25,10 @@
       accurate typing, specifically if they are tracking an array of values, destructuring those
       values in their `run` closure, and passing them on to typed APIs. Look out for `tsc` warnings.
 
+### ✨ Styles
+
+* Reset the `--xh-popup-bg` background color to match the primary `--xh-bg` color by default.
+
 ### 🐞 Bug Fixes
 
 * Fixed broken `Panel` resizing in Safari. (Other browsers were not affected.)

styles/vars.scss

@@ -644,7 +644,7 @@ body {
   //------------------------
   // Popups / dialogs
   //------------------------
-  --xh-popup-bg: var(--popup-bg, #ebf1f5);
+  --xh-popup-bg: var(--popup-bg, var(--xh-bg));
   --xh-popup-border-color: var(--popup-border-color, var(--xh-popup-title-bg));
   --xh-popup-border-width: var(--popup-border-width, var(--xh-border-width));
   --xh-popup-border-width-px: calc(var(--xh-popup-border-width) * 1px);
@@ -654,10 +654,6 @@ body {
   --xh-popup-title-font-size-px: calc(var(--xh-popup-title-font-size) * 1px);
   --xh-popup-title-text-color: var(--popup-title-text-color, var(--xh-title-text-color));
 
-  &.xh-dark {
-    --xh-popup-bg: var(--popup-bg, #293742);
-  }
-
   &.xh-mobile {
     --xh-popup-border-width: 2;
   }