Why panel control appear behind of the another control?

I wrote a functionality to open the panel when we click on the textbox. But the panel appears behind the other controls. The entire code should be written in C#, ASP.NET. Can anyone help me out with this?

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When I click on the "Dev Root Cause" text box, the panel should appear before the dropdown control. But it appears on the back side of the control.

When we click on the TextBox, one panel appears with the multi-checkbox list. But this should be appear before other controls.