Don't use opacity variable for default border color when borderOpacity is disabled

Author: adamwathan

src/plugins/borderColor.js

@@ -3,13 +3,21 @@ import withAlphaVariable from '../util/withAlphaVariable'
 
 export default function () {
   return function ({ addBase, matchUtilities, theme, variants, corePlugins }) {
-    addBase({
-      '*, ::before, ::after': withAlphaVariable({
-        color: theme('borderColor.DEFAULT', 'currentColor'),
-        property: 'border-color',
-        variable: '--tw-border-opacity',
-      }),
-    })
+    if (!corePlugins('borderOpacity')) {
+      addBase({
+        '*, ::before, ::after': {
+          'border-color': theme('borderColor.DEFAULT', 'currentColor'),
+        },
+      })
+    } else {
+      addBase({
+        '*, ::before, ::after': withAlphaVariable({
+          color: theme('borderColor.DEFAULT', 'currentColor'),
+          property: 'border-color',
+          variable: '--tw-border-opacity',
+        }),
+      })
+    }
 
     matchUtilities(
       {

tests/jit/opacity.test.css

@@ -1,8 +1,7 @@
 *,
 ::before,
 ::after {
-  --tw-border-opacity: 1;
-  border-color: rgba(229, 231, 235, var(--tw-border-opacity));
+  border-color: #e5e7eb;
 }
 * {
   --tw-shadow: 0 0 #0000;