Be a smart Kintone developer with Kintone UI Component.
It will support your UI customization project.
Use Case
Kintone UI Component allows you to create Kintone-like components easily. This library is useful to build Kintone customization and plug-in.
[ Sample code & the Button Component image ]

kintone.events.on('app.record.index.show', event => {
const Kuc = Kucs['1.x.x'];
const header = kintone.app.getHeaderMenuSpaceElement();
const buttonSubmit = new Kuc.Button({
text: 'Submit',
type: 'submit'
});
buttonSubmit.addEventListener('click', event => {
console.log(event);
});
const buttonAlert = new Kuc.Button({
text: 'Alert',
type: 'alert'
});
buttonAlert.addEventListener('click', event => {
console.log(event);
});
header.appendChild(buttonSubmit);
header.appendChild(buttonAlert);
});