Android support design library CoordinatorLayout w

I am using CoordinatorLayout with webview in my app. but I have a problem like the image:
on 4.4+. I don't know what's the problem with my layout.

this is my xml layout.

<?xml version="1.0" encoding="utf-8"?>
<android.support.v4.widget.SwipeRefreshLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/swipelayout"
    android:layout_width="match_parent"
    android:layout_height="match_parent">

    <android.support.design.widget.CoordinatorLayout xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:app="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="match_parent"
        android:fitsSystemWindows="true">

        <android.support.design.widget.AppBarLayout
            android:id="@+id/appbar"
            android:layout_width="match_parent"
            android:layout_height="256dp"
            android:theme="@style/ThemeOverlay.AppCompat.Dark.ActionBar">

            <android.support.design.widget.CollapsingToolbarLayout
                android:id="@+id/collapsing_toolbar"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:fitsSystemWindows="true"
                app:contentScrim="?attr/colorPrimary"
                app:expandedTitleMarginEnd="64dp"
                app:expandedTitleMarginStart="48dp"
                app:layout_scrollFlags="scroll|exitUntilCollapsed">

                <ImageView
                    android:id="@+id/backdrop"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:fitsSystemWindows="true"
                    android:scaleType="centerCrop"
                    app:layout_collapseMode="parallax" />

                <android.support.v7.widget.Toolbar
                    android:id="@+id/toolbar"
                    android:layout_width="match_parent"
                    android:layout_height="?attr/actionBarSize"
                    app:layout_collapseMode="pin"
                    app:popupTheme="@style/ThemeOverlay.AppCompat.Light" />

            </android.support.design.widget.CollapsingToolbarLayout>


        </android.support.design.widget.AppBarLayout>

        <android.support.v4.widget.NestedScrollView
            android:id="@+id/nsv_scroll"
            android:layout_width="match_parent"
            android:layout_height="match_parent"
            android:fitsSystemWindows="true"
            app:layout_behavior="@string/appbar_scrolling_view_behavior">

            <android.support.v7.widget.CardView
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:layout_margin="16dp">

                <WebView
                    android:id="@+id/webview"
                    style="@style/Widget.CardContent"
                    android:layout_width="match_parent"
                    android:layout_height="match_parent"
                    android:minHeight="100dp">


                </WebView>


            </android.support.v7.widget.CardView>

        </android.support.v4.widget.NestedScrollView>

        <com.getbase.floatingactionbutton.FloatingActionButton xmlns:fab="http://schemas.android.com/apk/res-auto"
            android:id="@+id/floatingaction"
            android:layout_width="wrap_content"
            android:layout_height="wrap_content"
            android:layout_margin="16dp"
            android:clickable="true"
            app:layout_anchor="@id/appbar"
            app:layout_anchorGravity="bottom|right|end"
            fab:fab_colorNormal="?attr/colorAccent"
            fab:fab_colorPressed="?attr/colorAccentDark" />

    </android.support.design.widget.CoordinatorLayout>
</android.support.v4.widget.SwipeRefreshLayout>

Expected layout: