AndroidStudio2.3.3 Error: Failed to resolve: com.android.support.constraint:constraint-layout:1.0.2

To use ConstraintLayout in your project, proceed as follows:

1. Ensure you have the "maven.google.com" repository declared in your module-level build.gradle file:

   repositories {
       maven {
           url 'https://maven.google.com'
       }
   }
   

2. Add the library as a dependency in the same build.gradle file:

   dependencies {
       compile 'com.android.support.constraint:constraint-layout:1.0.2'
   }
   

3. In the toolbar or sync notification, click Sync Project with Gradle Files.