Adding custom borders, background fills, and rounded corners to Android TextView elements without importing third-party UI libraries is achieved by defining vector <shape> XML drawables in res/drawable/.

Step 1: Create Shape Drawable XML

res/drawable/textview_border.xmlxml
<?xml version="1.0" encoding="utf-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android"
    android:shape="rectangle">
    
    <!-- Background Fill Color -->
    <solid android:color="#F8F9FA" />
    
    <!-- Border Width & Color -->
    <stroke
        android:width="2dp"
        android:color="#0066CC" />
        
    <!-- Rounded Corner Radius -->
    <corners android:radius="8dp" />
    
    <!-- Inner Padding -->
    <padding
        android:left="12dp"
        android:top="8dp"
        android:right="12dp"
        android:bottom="8dp" />
</shape>

Step 2: Apply Drawable to TextView in Layout XML

res/layout/activity_main.xmlxml
<TextView
    android:id="@+id/tvCustomBorder"
    android:layout_width="wrap_content"
    android:layout_height="wrap_content"
    android:text="Styled Border TextView"
    android:textColor="#333333"
    android:textSize="16sp"
    android:background="@drawable/textview_border" />