This part of the documentation will help you understand the Admin Structure.
1. Header Section : This is the default navbar section. It contains :
<div class="header-container container-xxl">
<header class="header navbar navbar-expand-sm expand-header">
..................
..................
..................
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</header>
</div>
2. Main Container Section : The main container section includes overlay, sidebar and main content section.
<div class="middle-content container-xxl p-0">
</div>
3. Sidebar : This is the sidebar code.
<!-- BEGIN SIDEBAR -->
<div class="sidebar-wrapper sidebar-theme">
<nav id="sidebar">
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................
</nav>
</div>
<!-- END SIDEBAR -->
4. Main Content : This is the Main Content code section.
<!-- BEGIN CONTENT AREA -->
<div id="content" class="main-content">
<div class="layout-px-spacing">
</div>
</div>
<!-- END CONTENT AREA -->