the status bar changes it's color to black inside fullscreen dialog fragment android

You have to set FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDSto indicate that this Window is responsible for drawing the background for the system bars.

if (Build.VERSION.SDK_INT >= Build.VERSION_CODES.LOLLIPOP) {
        dialog.getWindow().addFlags(WindowManager.LayoutParams.FLAG_DRAWS_SYSTEM_BAR_BACKGROUNDS);
        dialog.getWindow().setStatusBarColor(yourColor); 
    }

I just posted the solution to this problem here

Add following theme to res/value-v21/style

<style name="DialogTheme" parent="@style/Base.Theme.AppCompat.Light.Dialog">
     <item name="android:windowTranslucentStatus">true</item>
</style>

And then apply Style on DialogFragment in onCreate

@Override
public void onCreate(@Nullable Bundle savedInstanceState) {
    super.onCreate(savedInstanceState);
    setStyle(DialogFragment.STYLE_NO_TITLE, R.style.DialogTheme);
}

GUYS THE BEST SOLUTION IS IN THE WEBSITE LINK I AM POSTING HERE

https://zocada.com/android-full-screen-dialogs-using-dialogfragment/

I'll also upload the code here for reference

1st create a style FullScreenDialogStyle in your style file :

<style name="FullScreenDialogStyle" parent="Theme.AppCompat.Dialog">
    <item name="android:windowNoTitle">true</item>
    <item name="colorPrimaryDark">@color/colorPrimaryDark</item>
    <item name="colorPrimary">@color/colorPrimary</item>

    <!-- Set this to true if you want Full Screen without status bar -->
    <item name="android:windowFullscreen">false</item>

    <item name="android:windowIsFloating">false</item>

    <!-- This is important! Don't forget to set window background -->
    <item name="android:windowBackground">@color/colorWhite</item>

    <!-- Additionally if you want animations when dialog opening -->
    <!--<item name="android:windowEnterAnimation">@anim/slide_up</item>-->
    <!--<item name="android:windowExitAnimation">@anim/slide_down</item>-->
</style>

inside your dialogFragment class override a method onCreate

 @Override
    public void onCreate(@Nullable Bundle savedInstanceState) {
        super.onCreate(savedInstanceState);
        setStyle(DialogFragment.STYLE_NORMAL,R.style.FullScreenDialogStyle);

    }

then override Onstart method, through which u can access the getDialog() and set the height and width

@Override
public void onStart() {
    super.onStart();
    Dialog dialog = getDialog();
    if (dialog != null) {
        int width = ViewGroup.LayoutParams.MATCH_PARENT;
        int height = ViewGroup.LayoutParams.MATCH_PARENT;
        dialog.getWindow().setLayout(width, height);
    }
}