Change Gravity Forms Spinner to CSS Spinner

fnGravityFormSpinner.css

/* Spinner */
.gform_ajax_spinner {
	margin-left: 20px;
	border: 4px solid rgba(255, 255, 255, 0.3);
	border-left: 4px solid rgba(110, 73, 217, 0.7);
	animation: spinner 1.1s infinite linear;
	border-radius: 50%;
	width: 30px;
	height: 30px;
}

@keyframes spinner {
	0% { transform: rotate(0deg); }
	100% { transform: rotate(360deg); }
}

fnGravityFormSpinner.php

// Changes Gravity Forms Ajax Spinner (next, back, submit) to a transparent image
// this allows you to target the css and create a pure css spinner like the one used below in the style.css file of this gist.
function spinner_url( $image_src, $form ) {
	return  'data:image/gif;base64,R0lGODlhAQABAIAAAAAAAP///yH5BAEAAAAALAAAAAABAAEAAAIBRAA7'; // relative to you theme images folder
}
add_filter( 'gform_ajax_spinner_url', 'spinner_url', 10, 2 );