Событие jquery onmouseover не удалось запустить

Я упомянул какой-то сайт, например w3schools, но он показывает изменение изображения на событии onmouseover, здесь я хочу показать некоторую информацию в таблице, которая прозрачна, информация о разных кнопках на странице, как я могу сформировать код? я пробовал это:

 <script>
        function info(z) {
            z.style.visible = "true"
        }


            function defaultinfo(z) {
                z.style.display = "block"
            }


    </script>

<style>
.menu_box {
            background-color: #999;
            padding: 2px;
            color: #C0C0C0;
            opacity: .9;
            font-family: Garamond;
            font-size: xx-large;
            height: 91px;
            width: 1125px;
        }
</style>
<div id='cssmenu'>
        <ul>
<li><span><a href="StudentDetails.aspx" title="stud" onmouseover="info(this)"     onmouseout="defaultinfo(this)" visible="false">Students' Corner</a></span></li>
            <li><span><a href="FacultyDetails.aspx" onmouseover="info(this)" onmouseout="defaultinfo(this)" visible="false">Staff Room</a></span></li>
            <li><span><a href="LibWork.aspx" onmouseover="info(this)" onmouseout="defaultinfo(this)" visible="false">Librarian Workplace</a></span></li>
            <li><span><a href="AccountSection.aspx" onmouseover="info(this)" onmouseout="defaultinfo(this)" visible="false">Account Section</a></span></li>
            <li><span><a href="ContactUs.aspx" onmouseover="info(this)" onmouseout="defaultinfo(this)" visible="false">Contact Us</a></span></li>
            <li><span><a href="ControlPanel.aspx" onmouseover="info(this)" onmouseout="defaultinfo(this)" visible="false">ERP ControlPanel</a></span></li>
</ul>



<span class="menu_box" id="defaultinfo" style="color: #FFFFFF; font-size: medium; font-style: italic">For information on this page, role the cursor over the buttons.
            </span>
            <span class="menu_box" id="info" style="color: #FFFFFF; font-size: medium; font-style: italic">The students&#39; of saffrony institute of technology may use this button for their respective class notices,attendance and time-table. There are different modules such as &quot;library&quot; where students&#39; can reserve books or request which are unavailable, or modules like &quot;saffrony recycler&quot; where seniors can upload their used-books and sell them to juniors. There are even modules like &quot;student request&quot; where you can post your requests and &quot;student information&quot; where you can view and update your own requests.
            </span>