Step 1: Take one panel and all the content you want to collapse put into this panel.
Step 2: Set the Collapsed Property true.
Step 3: ExpandControlID/CollapseControlID : The Controls that will
expand or collapse the panel on a click, respectively. If these values
are the same, the panel will automatically toggle its state on each
click.
Step 4: TargetControlID is PanelID
Step 5: Select Panel and Set the Property SuppressPostBack="True"