Can not solve symbol 'Theme' in styles.xml file

You are giving the following error message:

Android Studio 3.2.1

build.gradle (Project: xxx) dependencies {classpath 'com.android.tools.build:gradle:3.1.2'}

I've tried the following:

1) I deleted the project .gradle directory 2) Build - > clean project 3) Build - > rebuild project (unsuccessful).

Should the Android Studio version be the same as build.gradle? If so, how do I upgrade?

Thank you in advance