如何通过groovy更新jenkins中的主题CSS的URL？

import jenkins.model.Jenkins
import jenkins.util.groovy.GroovyHookScript

def jenkins = Jenkins.getInstance()
def hookScript = new GroovyHookScript("""
    window.onload = function() {
        var cssUrl = 'https://example.com/custom.css'; // 自定义的CSS URL
        var styleTag = document.createElement('link');
        styleTag.rel = 'stylesheet';
        styleTag.href = cssUrl;
        document.head.appendChild(styleTag);
    };
""")
jenkins.getMarkupFormatter().getDescriptor().setHookScript(hookScript)
jenkins.save()