To customize Submit Button

Go to WP Customizer.

To customize Gray Tabs

Use following CSS (change color to yours):

.lrm-user-modal-container .lrm-switcher a { background: #adad34 !important; }

---

How to add custom CSS: https://www.wpbeginner.com/plugins/how-to-easily-add-custom-css-to-your-wordpress-site/