After building the project, add these dependencies in the dependencies{} block of build.gradle (Module:app). These are for Material Design, Retrofit, and RxJava:

// Design
implementation 'com.android.support:design:28.0.0'
implementation 'com.android.support:recyclerview-v7:28.0.0'
implementation 'com.android.support:cardview-v7:28.0.0'

// Retrofit
implementation "com.squareup.retrofit2:retrofit:$retrofit_version"
implementation "com.squareup.retrofit2:converter-gson:$retrofit_version"
implementation "com.squareup.retrofit2:adapter-rxjava2:$retrofit_version"
implementation "com.squareup.retrofit2:retrofit-converters:$retrofit_version"
implementation "com.squareup.retrofit2:retrofit-adapters:$retrofit_version"
implementation "com.squareup.okhttp3:logging-interceptor:$okhttp3_version"
implementation "com.google.code.gson:gson:$gson_version"

// Rx
implementation 'io.reactivex.rxjava2:rxandroid:2.0.2'
implementation 'io.reactivex.rxjava2:rxjava:2.2.0'