[EuiButtonEmpty] Revert xs size font size change

packages/eui/changelogs/upcoming/8930.md

@@ -0,0 +1,4 @@
+**Bug fixes**
+
+- Reverted a font-size change for `xs` buttons back to `12px`
+

packages/eui/src/components/form/form_control_layout/form_control_layout.styles.ts

@@ -224,7 +224,6 @@ export const euiFormControlLayoutSideNodeStyles = (
       ${buttons} {
         /* Override button hover/active transform */
         transform: none !important; /* stylelint-disable-line declaration-no-important */
-        line-height: 1; /* ensures correct vertical positioning of icons */
 
         /* Account for border around focusable children */
         &:focus-visible {

packages/eui/src/global_styling/mixins/_button.ts

@@ -394,7 +394,7 @@ export const euiButtonSizeMap = (euiThemeContext: UseEuiTheme) => {
       minWidth: euiTheme.base * (isRefreshVariant ? 6 : 7),
       height: euiTheme.size.l,
       radius: euiTheme.border.radius.small,
-      fontScale: isRefreshVariant ? ('s' as const) : ('xs' as const),
+      fontScale: 'xs' as const,
     },
     s: {
       minWidth: euiTheme.base * (isRefreshVariant ? 6 : 7),