diff --git a/src/index.ts b/src/index.ts
index 9681acb..88da47c 100644
--- a/src/index.ts
+++ b/src/index.ts
@@ -70,14 +70,18 @@ export function presetTheme<T extends Record<string, any>>(options: PresetThemeO
                   let themeValue
                     = getThemeVal(theme[key], themeKeys, index)
                     || (key === originalThemeKey ? getThemeVal(originalTheme, themeKeys) : null)
+                  let themeAlphaValue = '1'
                   if (themeValue) {
                     if (isColor) {
                       const cssColor = parseCssColor(themeValue)
+                      if (cssColor?.alpha !== undefined && cssColor?.alpha !== null)
+                        themeAlphaValue = `${cssColor.alpha}`
                       if (cssColor?.components)
                         themeValue = cssColor.components.join(' ')
                     }
                     obj[key] = {
                       [name]: themeValue,
+                      [`${name}--alpha`]: themeAlphaValue,
                     }
                   }
 
@@ -104,7 +108,7 @@ export function presetTheme<T extends Record<string, any>>(options: PresetThemeO
             if (isColor) {
               const cssColor = parseCssColor(val) || val
               if (typeof cssColor !== 'string')
-                curTheme[key] = wrapCSSFunction(cssColor.type, curTheme[key], cssColor?.alpha)
+                curTheme[key] = wrapCSSFunction(cssColor.type, curTheme[key], wrapVar(`${name}--alpha`))
             }
           }
           else {