Hello @Sneh bharti , you seem to be looking for help with K2?

Is that K2 On-Prem (aka K2 Five, aka Nintex Automation) or K2 Cloud (aka K2 Cloud) ?

Nintex Automation Cloud is a completely different product from K2 Five or K2 Cloud but you posted this under “Nintex Automation Cloud”

What exactly do you mean by “Custom code changes”, what are you trying to achieve?

The customization options for K2 Cloud, Nintex Automation and Nintex Automation Cloud are very different, so we first need to get on the same page as to which product you need help with please.

This One is for the k2 Five And by meaning of the custom code I mean to say that for text area or text box if I want to chance the text box design by css code or by anything how can I achieve this thing 

Hello @Sneh bharti , to load custom css you can just use a label or data label control and check the literal check box, if you use a data label also uncheck the prevent xss checkbox.

Then, just set the label to inline css html code for example:

<style>
.theme-entry input.SFC.SourceCode-Forms-Controls-Web-TextBox {
    color: red;
    border: 3px solid #FF6D00;
    border-radius: 5px;
    padding: 5px;
    box-shadow:none;
    background-color: #FED1B0;
}
</style>

I would recommend that you set the text or load the text for the label in a server rule as a best practice.

Developer tools help here to insect the classes or names of various controls so you can target them with css.

This does require that you a very good understanding of the CSS language and rules.