如何保持div文件的头文件固定在另一个文件的固定div之上？

This is the header file.I want to keep the div "header" fixed.

<div id="header" style="display:block;">
  <table  style="width:100%">
    <tr>
        <td class="col-sm-6" style="background-color:lavender;"><a href = "<?php echo base_url();?>index.php/cust"><h1>Customer</h1></a></td>
        <td class="col-sm-6" style="background-color:lavenderblush;"><a href = "<?php echo base_url();?>index.php/custgroup"><h1>Customer Groups</h1></a></td>
    </tr>   
  </table>
 </div>

This is the content file with another fixed block "content"

<div id="content" style="position:fixed;background:lavender; width:100%;">
    <form action="<?php echo base_url(); ?>index.php/cust/add" method="post" class="form-inline col-sm-12">
    <div class="form-group col-sm-2">
    <label class="sr-only" for="name">Name:</label>
    <input type="text" name="name" class="form-control" placeholder="Enter Name"/>
    </div>
    <div class="form-group col-sm-2">
    <label class="sr-only" for="age">Age:</label>
    <input type="text" name="age" class="form-control" placeholder="Enter Age"/>
    </div>
    <div class="form-group col-sm-2">
    <input type="submit" value="Add new customer">
    </div>
    </form>
    </div>

I call these two files in a php code

 $this->load->view('header');
     $this->load->view('Cust_view',$data);
     $this->load->view('footer');

The "content" div overlaps the "header" div, whereas i need "content" to be below "header", both fixed. Kindly help.

Make a Main-Div and put Header-Div and Content-Div into it.

CSS

<style type="text/css">
 div#main {
  position: absolute;
  top: 0; 
  right: 0;
  bottom: 0; // if you like to have a full-screen-Div.
  left: 0;
</style>

HTML:

<div id="main">
 <div id="header">
  foo
 </div>
 <div id="contente">
  foo
 </div>
</div>