How to Inject Custom CSS into a NetSuite Record Form Header

1. Host the Custom CSS File: Upload your custom CSS file and any associated images to the NetSuite File Cabinet. Ensure that the file's availability is set to "Available Without Login" to allow public access.

2. Create a User Event Script: Develop a new user event script in SuiteScript 2.x. This script will execute during the beforeLoad event of the target record form.

javascript
/**
 * @NApiVersion 2.x
 * @NScriptType UserEventScript
 */
define([], function() {
    function beforeLoadTestInject(context) {
        var form = context.form;
        var cssScriptField = form.addField({
            id: 'custpage_cssfield',
            type: 'inlinehtml',
            label: 'Custom CSS Injector'
        });
        cssScriptField.defaultValue = "<script type="text/javascript">var linkElement = document.createElement('link');linkElement.rel = 'stylesheet';linkElement.href = 'https://system.sandbox.netsuite.com/core/media/media.nl?id=577&c=05801&h=F4390276d84372784aa&_xt.css';document.getElementsByTagName('head')[0].insertBefore(linkElement,document.getElementsByTagName('head')[0].firstChild);</script>";
    }
    return {
        beforeLoad: beforeLoadTestInject
    };
});

The script above creates an inline HTML field (custpage_cssfield) on the record form. The defaultValue of this field contains a JavaScript snippet. This JavaScript dynamically creates a ` element for a stylesheet and inserts it as the first child within the ` section of the HTML document. This ensures the custom CSS loads early in the page rendering process. It is important to note that this method involves direct Document Object Model (DOM) manipulation, which NetSuite documentation explicitly advises against, recommending the use of SuiteScript APIs for UI interactions. Additionally, NetSuite has indicated that inline HTML fields on standard record forms, outside of Suitelets, are subject to deprecation in a future release. Therefore, this approach should be considered a short-term solution and used with caution, as it may lead to unexpected behavior or require adjustments in future NetSuite versions.