Bug 1656004: Change padding for option to match the non-native theming spec. r=emilio

Differential Revision: https://phabricator.services.mozilla.com/D85303

layout/reftests/w3c-css/submitted/contain/contain-size-select-elem-005-ref.html

@@ -7,6 +7,10 @@
   <style>
   select {
     color: transparent;
+    /* We make scrollbars transparent because some <option> elements can cause
+       overflow, which can cause scrollbars to be active in the test and
+       inactive in the reference.  But the test only cares about the sizing. */
+    scrollbar-color: transparent transparent;
   }
   .fsMedium {
     /* custom styling for some select elements, which is allowed to influence

layout/reftests/w3c-css/submitted/contain/contain-size-select-elem-005.html

@@ -10,6 +10,10 @@
   select {
     contain: size;
     color: transparent;
+    /* We make scrollbars transparent because some <option> elements can cause
+       overflow, which can cause scrollbars to be active in the test and
+       inactive in the reference.  But the test only cares about the sizing. */
+    scrollbar-color: transparent transparent;
   }
   .fsMedium {
     /* custom styling for some select elements, which is allowed to influence

layout/style/res/forms.css

@@ -321,6 +321,7 @@ option {
   float: none !important;
   position: static !important;
   min-block-size: 1em;
+  padding-block: 2px;
   /*
    * Note that the "UA !important" tests in
    * layout/style/test/test_animations.html depend on this rule, because
@@ -336,8 +337,7 @@ option {
 }
 
 select > option {
-  padding-block: 0;
-  padding-inline: 3px 5px;
+  padding-inline: 4px;
 }
 
 option:checked {

testing/web-platform/tests/css/vendor-imports/mozilla/mozilla-central-reftests/contain/contain-size-select-elem-005-ref.html

@@ -7,6 +7,10 @@
   <style>
   select {
     color: transparent;
+    /* We make scrollbars transparent because some <option> elements can cause
+       overflow, which can cause scrollbars to be active in the test and
+       inactive in the reference.  But the test only cares about the sizing. */
+    scrollbar-color: transparent transparent;
   }
   .fsMedium {
     /* custom styling for some select elements, which is allowed to influence

testing/web-platform/tests/css/vendor-imports/mozilla/mozilla-central-reftests/contain/contain-size-select-elem-005.html

@@ -10,6 +10,10 @@
   select {
     contain: size;
     color: transparent;
+    /* We make scrollbars transparent because some <option> elements can cause
+       overflow, which can cause scrollbars to be active in the test and
+       inactive in the reference.  But the test only cares about the sizing. */
+    scrollbar-color: transparent transparent;
   }
   .fsMedium {
     /* custom styling for some select elements, which is allowed to influence