drop withAlpha on theme (#9906)

src/lib/setupContextUtils.js

@@ -253,25 +253,18 @@ function buildPluginApi(tailwindConfig, context, { variantList, variantMap, offs
   }
 
   function resolveThemeValue(path, defaultValue, opts = {}) {
-    const [pathRoot, ...subPaths] = toPath(path)
-    const value = getConfigValue(['theme', pathRoot, ...subPaths], defaultValue)
-    return transformThemeValue(pathRoot)(value, opts)
+    let parts = toPath(path)
+    let value = getConfigValue(['theme', ...parts], defaultValue)
+    return transformThemeValue(parts[0])(value, opts)
   }
 
-  const theme = Object.assign(
-    (path, defaultValue = undefined) => resolveThemeValue(path, defaultValue),
-    {
-      withAlpha: (path, opacityValue) => resolveThemeValue(path, undefined, { opacityValue }),
-    }
-  )
-
   let variantIdentifier = 0
   let api = {
     postcss,
     prefix: applyConfiguredPrefix,
     e: escapeClassName,
     config: getConfigValue,
-    theme,
+    theme: resolveThemeValue,
     corePlugins: (path) => {
       if (Array.isArray(tailwindConfig.corePlugins)) {
         return tailwindConfig.corePlugins.includes(path)