By adding style to your layouts you can round them

Define this in drawable :

<?xml version="1.0" encoding="UTF-8"?>
<shape xmlns:android="http://schemas.android.com/apk/res/android">
    <solid android:color="#FFFFFF"/>
    <stroke android:width="3dip" android:color="#B1BCBE" />
    <corners android:radius="10dip"/>
    <padding android:left="0dip" android:top="0dip" android:right="0dip" android:bottom="0dip" />
</shape>

and add above style to the backround of your layout

android:background="@drawable/your_above_syle"

Another way is adding 9 patch images to the background of your layouts for example using this image which can round and add shadow to your layouts

xml code: list_item

<?xml version="1.0" encoding="utf-8"?>
<RelativeLayout xmlns:android="http://schemas.android.com/apk/res/android"
    android:id="@+id/parent_relativeLayout"
    android:layout_width="match_parent"
    android:layout_height="270dp">

    <android.support.v7.widget.CardView xmlns:android="http://schemas.android.com/apk/res/android"
        xmlns:card_view="http://schemas.android.com/apk/res-auto"
        android:layout_width="match_parent"
        android:layout_height="wrap_content"
        android:layout_marginTop="10dp"
        android:clickable="true"
        card_view:cardBackgroundColor="@android:color/black"
        card_view:cardCornerRadius="5dp"
        card_view:cardElevation="0dp"
        card_view:cardPreventCornerOverlap="false"
        card_view:cardUseCompatPadding="true">


        <com.google.android.youtube.player.YouTubeThumbnailView
            android:id="@+id/youtube_thumbnail"
            android:layout_width="match_parent"
            android:layout_height="250dp"
            android:scaleType="centerCrop"
            android:visibility="visible" />

        <RelativeLayout
            android:id="@+id/relativeLayout_over_youtube_thumbnail"
            android:layout_width="match_parent"
            android:layout_height="250dp"
            android:visibility="visible">

            <ImageView
                android:id="@+id/btnYoutube_player"
                android:layout_width="match_parent"
                android:layout_height="match_parent"
                android:scaleType="center"
                android:src="@android:drawable/btn_plus" />
            <TextView
                android:id="@+id/videosTitle_tv"
                android:layout_width="match_parent"
                android:layout_height="40dp"
                android:text="Vidoes title here"
                android:gravity="center"
                android:layout_alignParentBottom="true"/>
        </RelativeLayout>
    </android.support.v7.widget.CardView>


</RelativeLayout>

RecyclerAdapter

package com.mobileappdev.videosapp.adapter;

import android.app.Activity;
import android.content.Context;
import android.content.Intent;
import android.content.res.Resources;
import android.support.v7.widget.RecyclerView;
import android.view.LayoutInflater;
import android.view.View;
import android.view.ViewGroup;
import android.widget.ImageView;
import android.widget.RelativeLayout;
import android.widget.TextView;

import com.google.android.youtube.player.YouTubeInitializationResult;
import com.google.android.youtube.player.YouTubeStandalonePlayer;
import com.google.android.youtube.player.YouTubeThumbnailLoader;
import com.google.android.youtube.player.YouTubeThumbnailView;
import com.mobileappdev.videosapp.R;

/**
 * Created by ofaroque on 8/13/15.
 */
public class RecyclerAdapter extends RecyclerView.Adapter<RecyclerAdapter.VideoInfoHolder> {

    //these ids are the unique id for each video
    String[] VideoID = {"P3mAtvs5Elc", "nCgQDjiotG0", "P3mAtvs5Elc"};
    String[] Ttitles = {"Video # 1", "Video # 2", "Video # 3"};
    Context ctx;
    private static String KEY = "Add your authentication key for google";

    public RecyclerAdapter(Context context) {
        this.ctx = context;
    }

    @Override
    public VideoInfoHolder onCreateViewHolder(ViewGroup parent, int viewType) {
        View itemView = LayoutInflater.from(parent.getContext()).inflate(R.layout.list_item, parent, false);
        return new VideoInfoHolder(itemView);
    }

    @Override
    public void onBindViewHolder(final VideoInfoHolder holder, final int position) {


        final YouTubeThumbnailLoader.OnThumbnailLoadedListener onThumbnailLoadedListener = new YouTubeThumbnailLoader.OnThumbnailLoadedListener() {
            @Override
            public void onThumbnailError(YouTubeThumbnailView youTubeThumbnailView, YouTubeThumbnailLoader.ErrorReason errorReason) {

            }

            @Override
            public void onThumbnailLoaded(YouTubeThumbnailView youTubeThumbnailView, String s) {
                youTubeThumbnailView.setVisibility(View.VISIBLE);
                holder.relativeLayoutOverYouTubeThumbnailView.setVisibility(View.VISIBLE);
            }
        };

        holder.youTubeThumbnailView.initialize(KEY, new YouTubeThumbnailView.OnInitializedListener() {
            @Override
            public void onInitializationSuccess(YouTubeThumbnailView youTubeThumbnailView, YouTubeThumbnailLoader youTubeThumbnailLoader) {

                youTubeThumbnailLoader.setVideo(VideoID[position]);

                youTubeThumbnailLoader.setOnThumbnailLoadedListener(onThumbnailLoadedListener);
                holder.videosTitleTextView.setText(Ttitles[position]);
            }

            @Override
            public void onInitializationFailure(YouTubeThumbnailView youTubeThumbnailView, YouTubeInitializationResult youTubeInitializationResult) {
                //write something for failure
            }
        });
    }

    @Override
    public int getItemCount() {
        return VideoID.length;
    }

    public class VideoInfoHolder extends RecyclerView.ViewHolder implements View.OnClickListener {

        protected RelativeLayout relativeLayoutOverYouTubeThumbnailView;
        YouTubeThumbnailView youTubeThumbnailView;
        protected ImageView playButton;
        protected TextView videosTitleTextView;

        public VideoInfoHolder(View itemView) {
            super(itemView);
            playButton = (ImageView) itemView.findViewById(R.id.btnYoutube_player);
            videosTitleTextView = (TextView) itemView.findViewById(R.id.videosTitle_tv);
            playButton.setOnClickListener(this);
            relativeLayoutOverYouTubeThumbnailView = (RelativeLayout) itemView.findViewById(R.id.relativeLayout_over_youtube_thumbnail);
            youTubeThumbnailView = (YouTubeThumbnailView) itemView.findViewById(R.id.youtube_thumbnail);
        }

        @Override
        public void onClick(View v) {

            Intent intent = YouTubeStandalonePlayer.createVideoIntent((Activity) ctx, KEY, VideoID[getLayoutPosition()]);
            ctx.startActivity(intent);
        }
    }
}

MainActivity

 package com.mobileappdev.videosapp;

    import android.support.v7.app.AppCompatActivity;
    import android.os.Bundle;
    import android.support.v7.widget.LinearLayoutManager;
    import android.support.v7.widget.RecyclerView;
    import android.util.Log;

    import com.google.firebase.database.DataSnapshot;
    import com.google.firebase.database.DatabaseError;
    import com.google.firebase.database.DatabaseReference;
    import com.google.firebase.database.FirebaseDatabase;
    import com.google.firebase.database.ValueEventListener;
    import com.mobileappdev.videosapp.adapter.RecyclerAdapter;
    import com.mobileappdev.videosapp.models.Videos;

    public class MainActivity extends AppCompatActivity {

        private static String TAG = MainActivity.class.getSimpleName();


        @Override
        protected void onCreate(Bundle savedInstanceState) {
            super.onCreate(savedInstanceState);
            setContentView(R.layout.activity_main);


            RecyclerView recyclerView = (RecyclerView) findViewById(R.id.recyclerView);
            recyclerView.setHasFixedSize(true);
            //to use RecycleView, you need a layout manager. default is LinearLayoutManager
            LinearLayoutManager linearLayoutManager = new LinearLayoutManager(this);
            linearLayoutManager.setOrientation(LinearLayoutManager.VERTICAL);
            recyclerView.setLayoutManager(linearLayoutManager);
            RecyclerAdapter adapter = new RecyclerAdapter(this);
            recyclerView.setAdapter(adapter);

        }
    }

I was testing out a new browser and wondering why it showed videos list in grid mode, while my previous browser had it in list mode (the way I like). You can change it to list mode by editing cookie PREF, and adding &cvdm=list to it.