What's wrong with the button?

Question

Android

<Button
        android:id="@+id/button"
        android:layout_width="120dp"
        android:layout_height="40dp"
        android:layout_gravity="center_horizontal"
        android:layout_marginTop="@dimen/marginSize"
        android:fontFamily="@font/roboto"
        android:text="@string/ready"
        android:textColor="@color/black"
        android:textFontWeight="@android:integer/config_longAnimTime"
        app:backgroundTint="@color/green" />

The button is 120dp wide, i.e. 1/3 of the screen, but is displayed in full screen width
Kotlin is not associated with this button

Answer 1

Everything is ok with the button. Something is wrong somewhere else.

Answer 2

The syntax is OK. Where is it displayed in full screen width? In preview when designing in the studio or in a running application?