For activities in full screen mode, android:windowSoftInputMode="adjustResize" will not work.
https://developer.android.com/reference/android/view/WindowManager.LayoutParams.html#FLAG_FULLSCREEN
A fullscreen window will ignore a value of SOFT_INPUT_ADJUST_RESIZE for the window's softInputMode field; the window will stay fullscreen and will not resize.
I use the following method in the activity to resize the layout by setting a bottom padding:
    public void adjustResizeOnGlobalLayout(@IdRes final int viewGroupId, final WebView webView) {
        final View decorView = getWindow().getDecorView();
        final ViewGroup viewGroup = (ViewGroup) findViewById(viewGroupId);
        decorView.getViewTreeObserver().addOnGlobalLayoutListener(new ViewTreeObserver.OnGlobalLayoutListener() {
            public void onGlobalLayout() {
                DisplayMetrics displayMetrics = getResources().getDisplayMetrics();
                Rect rect = new Rect();
                decorView.getWindowVisibleDisplayFrame(rect);
                int paddingBottom = displayMetrics.heightPixels - rect.bottom;
                if (viewGroup.getPaddingBottom() != paddingBottom) {
                    // showing/hiding the soft keyboard
                    viewGroup.setPadding(viewGroup.getPaddingLeft(), viewGroup.getPaddingTop(), viewGroup.getPaddingRight(), paddingBottom);
                } else {
                    // soft keyboard shown/hidden and padding changed
                    if (paddingBottom != 0) {
                        // soft keyboard shown, scroll active element into view in case it is blocked by the soft keyboard
                        webView.evaluateJavascript("if (document.activeElement) { document.activeElement.scrollIntoView({behavior: \"smooth\", block: \"center\", inline: \"nearest\"}); }", null);
                    }
                }
            }
        });
    }