Android StudioでのbuildToolsVersion,miniSdkVersion,compileSdkVersion,targetSdkVersionのバージョン設定の問題

    compileSdkVersion 26        //  Gradle      SDK        ，      
    buildToolsVersion "28.0.2"  //    sdkbuildtools     
    defaultConfig {
        minSdkVersion 21        //           ，     ，      
        targetSdkVersion 26     //<=compileSdkVersion，         ，      compileSdkVersion      ，           
        versionCode 1
        versionName "1.0"

        testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"

    }

implementation 'com.android.support:appcompat-v7:26.1.0'   // compileSdkVersion  
implementation 'com.android.support:design:26.1.0'         // compileSdkVersion