[IMP] portal, website: change the default website body bg

Use a very very very light gray as body background color for
the website so that default white cards have some contrast with the
body. Also adapt the portal system to use the portal colors when the
body bg color is equal to that very very very light gray (while it was
compared to $white before).

closes odoo/odoo#29318

addons/portal/static/src/scss/bootstrap_overridden.scss

@@ -3,6 +3,12 @@ $sizes: (
     0: 0,
 );
 
+// Body
+//
+// Settings for the `<body>` element.
+
+$body-bg: $o-portal-default-body-bg;
+
 // Fonts
 //
 // Font, line-height, and color for body text, headings, and more.

addons/portal/static/src/scss/portal.scss

@@ -21,7 +21,7 @@ $o-portal-table-td-pb: map-get($spacers, 1) !default; // bts4 pb-1
 $o-portal-bg-color: desaturate($gray-200, 100%);
 
 // Check if portal uses default colors
-$o-portal-use-default-colors: $body-bg == $white;
+$o-portal-use-default-colors: $body-bg == $o-portal-default-body-bg;
 
 // Frontend general
 #wrapwrap {

addons/portal/static/src/scss/primary_variables.scss

@@ -0,0 +1 @@
+$o-portal-default-body-bg: #FCFCFC;

addons/website/static/src/scss/bootstrap_overridden.scss

@@ -18,7 +18,9 @@ $yiq-text-dark: if($-is-light, null, color('text'));
 //
 // Settings for the `<body>` element.
 
-$body-bg: color('body');
+@if color('body') { // Do not default to bootstrap but to the portal value
+    $body-bg: color('body');
+}
 $body-color: color('text');
 
 // Fonts

addons/website/static/src/scss/primary_variables.scss

@@ -8,7 +8,7 @@ $o-theme-layout: 'full';
 $-palettes: ();
 @each $palette in $o-color-palettes {
     $-palettes: append($-palettes, map-merge((
-        'body': null, // Default to bootstrap
+        'body': $o-portal-default-body-bg,
         'menu': #F9F9F9,
         'footer': #F9F9F9,
         'text': null, // Default to bootstrap