If you want to change this button styling for a specific dialog, then you have to add your own styling into this core file JoomlaFolder/components/com_easysocial/themes/wireframe/profile/dialogs/dialog.user.ban.php

Then you can copy this file and place this file into your current template new directory folder JoomlaFolder/templates/yourCurrentTemplate/html/com_easysocial/profile/dialogs/dialog.user.ban.php

Hello. There is no way to change colour with CSS? Thanks.

Can, but it will affect to other dialog button styling.

body #es.es-dialog .es-dialog-footer-content .btn[data-close-button] {

	background-color: #9ea9ca !important;

}