This is my dependencies file and there is an underlined red colored text on the compile 'com.android.support:appcompat-v7.27.1.1'
apply plugin: 'com.android.application'
 android {
compileSdkVersion 27
defaultConfig {
    applicationId "com.abc.mcaproject"
    minSdkVersion 21
    targetSdkVersion 27
    versionCode 1
    versionName "1.0"
    testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
}
buildTypes {
    release {
        minifyEnabled false
        proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
    }
}
}
dependencies {
implementation fileTree(dir: 'libs', include: ['*.jar'])
compile 'com.android.support:appcompat-v7.27.1.1'
implementation 'com.android.support.constraint:constraint-layout:1.1.0'
implementation 'com.google.firebase:firebase-database:11.6.0'
implementation 'com.google.firebase:firebase-messaging:11.6.0'
implementation 'com.google.firebase:firebase-auth:11.6.0'
implementation 'com.google.firebase:firebase-storage:11.6.0'
testImplementation 'junit:junit:4.12'
androidTestImplementation 'com.android.support.test:runner:1.0.2'
androidTestImplementation 'com.android.support.test.espresso:espresso- 
core:3.0.2'
}
apply plugin: 'com.google.gms.google-services'
This because of this I am having problems changing themes in the styles.xml
 
     
    
 
     
     
    