On page load event we define button css properties
Protected Sub Page_Load(ByVal sender As Object, ByVal e As System.EventArgs)
Handles Me.Load
'define control css
ValidatUser.Attributes.Add("class", "btnSubmit")
vUsername.Attributes.Add("class", "txtBox")
'on post back page we change the state of control
If Page.IsPostBack Then
'hide validate button
ValidateUser.Visible = False
'disable textbox
vUsername.Enabled = False
End If
End Sub
I hope you get the idea.