wp-calypso/client/signup/steps/site/style.scss

input[type="text"].site_site-url.form-text-input {
	padding-right: 122px;
}

.site__wordpress-domain-suffix {
	color: var(--color-neutral-light);
	line-height: 40px;
	margin-left: -122px;
	pointer-events: none;
	position: absolute;
}