How to change css class in code behind in vb.net

Question

<div id="test" class="search-bar-inner-container">

 

i need to change this class="search-bar-inner-container"  for id 'test'  in code behind of vb.net file

so i tried like below

Protected test As As HtmlControls.HtmlGenericControl

 

test.Attributes.Add("class", "search-bar-inner-container1") 

 

but its showing null error