Magento 2.0 override admin css

you need to add a custom module and define css in desired xml or if you want to add in all pages create default.xml 1) add a module Ex. Emizentech/NewAdmin 2) create a new file view/adminhtml/layout/default.xml in the module

Magento 2 – How to add color picker in admin configuration options?

Create system.xml at Below Path app/code/Emizentech/Newsletter/etc/adminhtml

Create Color.php File at below Path

Add color picker CSS library: Create adminhtml_system_config_edit.xml at Below Path app/code/Emizentech/Newsletter/view/adminhtml/layout