为PHP添加的DIV标记添加边距

我想给这个<div>:添加边距

$notification_list .= "
    <div class='FriendRdiv'>
        <a href='main.php?u=".$initiator."'>
            <img src='../img/".$pr."' id='FriendRPP'>
        </a>
        <a id='FriendRfrom'>".$initiator." sent you a friend request</a>
    </div>
    <form class='FriendRForm Rejecat' onsubmit='return false'>
        <input type='submit' value='Reject' id='Reject'>
    </form>         
    <form class='FriendRForm' onsubmit='return false'>
         <input type='submit' value='Accept' id='Accept'>
    </form>";

我不知道我会收到多少通知，所以我希望每个<div>都比之前有更大的裕度。