add property to css class by using css classname in c#

In Javascript do like this

document.getElementById(id).style.property=new style

for more http://www.w3schools.com/js/js_htmldom_css.asp

hi muthukumar
 
Your question is need to be little bit clear.

Approaching editing css class is not best practice though it's not possible too.
Because css is not meant for user depended, is applicable for whole website wherever u referred them, If you change the css from c# it will affect the other user who is not required that property to view or use.

1. Do you want to add inline style to img tag using C# ?

If so



access this img1 from your code behind.

 img1.attributes.add("style","display:none");

  2. Another method is create a css class with display:none property
 
  img1.attributes.add("class","
ui-datepicker-trigger");   

[If this solutions is works, like it]

id="img1" runat="server"  title="" alt="" src="/_layouts/15/images/calendar.png" class="ui-datepicker-trigger">

img1.Style.Add("display","none");