<form method="post" onsubmit="msg-student-delete.php" action="" >

        <div>
                <a class="btn btn-default" href="msg-student-sent.php">
                    <span class="glyphicon glyphicon-envelope"></span>
                    <span class="glyphicon glyphicon-arrow-right"></span>
                    <span class="glyphicon glyphicon-user"></span>

                </a>

                <button type="sumbit" class="btn btn-danger" onClick="ask_box()" >
                    <span class="glyphicon glyphicon-remove"></span>
                    <span class="glyphicon glyphicon-envelope"></span>
                </button>
                <!-- 確認視窗的script-->
                <script>
                function ask_box(){
                        if(confirm("確認刪除嗎?")){

                        }else{

                        }
                }
                </script>
                <!-- 確認視窗的script結束-->
</form>