Update PST scss (#470)

Author: jarrodmillman

assets/theme-css/pst/components/_breadcrumbs.scss

@@ -12,7 +12,7 @@ ul.bd-breadcrumbs {
 
   li.breadcrumb-item {
     display: flex;
-    align-items: baseline;
+    align-items: center;
 
     // Style should look like heavier in-page links
     // keeping visited in the default link colour

assets/theme-css/pst/variables/_color.scss

@@ -310,6 +310,7 @@ html:not([data-theme]) {
 @each $mode in (light, dark) {
   html[data-theme="#{$mode}"] {
     @include theme-colors($mode);
+    color-scheme: $mode;
   }
 }