我的网站有问题。当我缩小时，侧边栏会移动到我的主要内容下方。这是网站。这是我的代码，
<div id="content_main" >
<div id="content_center">
<div id="news_spotlight_container">
<div class="news">
<h2 style=" border-bottom: 6px solid #000000; letter-spacing: 2px;color: #565347; ">WELCOME</h2>
<div class="newsitem">
<br class="clear">
<h3><a href="#" ><img src="CIS_files/cis_view.png" class="image_news" alt="[ Read Story: X-ray laser ]">Message From Chair Person</a></h3>
<p>Thankyou students.Thankyou students.Thankyou students.Thankyou students.Thankyou students.Thankyou students.Thankyou students.Thankyou is si si sissi iss is is iss i students.Thankyou students.Thankyou students.Thankyou students.Thankyou students.Thankyou. </p>
</div>
<br class="clear">
<div class="newsitem">
<h3><a href="#" ><img src="CIS_files/cis_view.png" class="image_news" alt="[ Read Story: X-ray laser ]">Research</a></h3>
<p>Thankyou students.Thankyou students.Thankyou students.Thankyou students.Thankyou students.Thankyou students.Thankyou students.Thankyou is si si sissi iss is is iss i students.Thankyou students.Thankyou students.Thankyou students.Thankyou students.Thankyou.</p>
</div>
<br class="clear">
<div class="newsitem">
<h3><a href="#" ><img src="CIS_files/cis_view.png" class="image_news" alt="[ Read Story: X-ray laser ]">Extra Curricular Activities</a></h3>
<p>Thankyou students.Thankyou students.Thankyou students.Thankyou students.Thankyou students.Thankyou students.Thankyou students.Thankyou is si si sissi iss is is iss i students.Thankyou students.Thankyou students.Thankyou students.Thankyou students.Thankyou.</p>
</div>
<br class="clear">
</div> <!-- End news -->
<div id="more-stories">
<div>
<h2 style="border-bottom: 6px solid #000000; letter-spacing: 2px; margin-bottom: 10px;">Quick Links</h2>
</div>
<ul id="newslinks">
<li><a href="#">BE Time Table</a></li>
<li><a href="#">Lab Workbooks</a></li>
<li><a href="#">Final Year Projects</a></li>
<li><a href="#">Contact Us</a></li>
</ul>
</div>
<div id="more-stories">
<div>
<h2 style="border-bottom: 6px solid #000000; letter-spacing: 2px; margin-bottom: 10px;">Hall of Fame</h2>
</div>
<ul id="newslinks">
<li><a href="#">Shams Uddin</a></li>
<li><a href="#">Fahad Qasim</a></li>
<li><a href="#">Zain Akhtar</a></li>
</ul>
</div>
<div id="more-stories">
<div>
<h2 style="border-bottom: 6px solid #000000; letter-spacing: 2px; margin-bottom: 10px;">Events</h2>
</div>
<ul id="newslinks">
<li><a href="#">TechElete</a></li>
<li><a href="#">Vision</a></li>
<li><a href="#">Poster Competition</a></li>
<li><a href="#">Cache</a></li>
</ul>
</div>
<p><!-- End more-stories -->
<br class="clear">
</p>
<div style="width:100%; border-right:0px;" class="news" >
<h2 style=" border-bottom: 6px solid #000000 ;
letter-spacing: 2px;
">
<a href="#">About CISE</a>
</h2>
<br class="clear">
<img class="image_news" src="CIS_files/cis_view.png" alt="cis view" />
<p>The department of Computer Information & Systems Engineering (CISE) was established in July 1997. The department has been a pioneer at NED University in many respects. We have set trends that have been followed by many other departments. <br><br>Currently, the department offers a four year bachelors program in morning and masters program in morning as well in evening.</p>
</div>
</div> <!-- End news_spotlight_container -->
<br class="clear">
</div><!-- End content_center -->
</div> <!-- End content_main -->