Copy and paste of player css from inspecting the player on my site, where I use the Sixteen - Nine Pro theme. (just fyi)

custom.css

/* Podcast player */
.site-container .rm-player {
	font-family: Helvetica, sans-serif;
	margin-bottom: 25px;
	margin-top: 25px;
}

.site-container .rm-player .audio-title {
	color: #333;
	font-size: 22px;
	margin-bottom: 10px;
	line-height: 1.35;
	overflow: hidden;
}

.site-container .rm-player .audio-title small {
	color: #aaa;
	display: block;
	font-size: 11px;
	font-weight: bold;
	letter-spacing: 2px;
	margin-bottom: 5px;
	margin-top: 7px;
	text-transform: uppercase;
}

.site-container .rm-player .rm-player-image {
	float: left;
	height: 100px;
	clear: both;
	margin: 0 20px 0 0;
	padding: 0;
	line-height: 0;
	width: 100px;
}

.site-container .rm-player .rm-player-image img {
	height: auto;
	max-width: 100%;
}

.site-container .rm-player .rm-player-controls {
	display: block;
	position: relative;
}

.site-container .rm-player button {
	box-shadow: none;
	margin: 0;
	text-shadow: none;
}

.site-container .rm-player .share-button {
	background: #f5f5f5;
	border-radius: 0px;
	border: none;
	bottom: 0;
	color: #aaa;
	font-family: Helvetica, sans-serif;
	font-size: 12px;
	font-weight: normal;
	height: 50px;
	outline: none;
	line-height: 1;
	letter-spacing: 0;
	padding: 0;
	position: absolute;
	right: 0px;
	text-align: center;
	text-transform: lowercase;
	width: 9.5%;
}

.site-container .rm-player .share-button:before {
	content: "\f242";
	color: #333;
	display: block;
	font-family: "dashicons";
	font-size: 24px;
	font-weight: normal;
	margin-bottom: 2px;
	-webkit-font-smoothing: antialiased;
	-moz-osx-font-smoothing: grayscale;
}

.site-container .rm-player .share-button:hover {
	background: #eee;
}

.site-container .rm-player .share-button.opened:before {
	content: "\f335";
}

.site-container .rm-player .audio-share {
	background: #f5f5f5;
	border-bottom: 2px solid #fff;
	bottom: 50px;
	display: none;
	padding: 10px 20px;
	position: absolute;
	right: 0px;
	width: 100%;
	z-index: 9999;
}

.site-container .rm-player .audio-share ul,
.site-container .rm-player .audio-share ul li {
	list-style: none;
	margin: 0;
	padding: 0;
}

.site-container .rm-player .audio-share ul li {
	display: block;
	border-bottom: 1px solid #ddd;
	vertical-align: middle;
	padding: 10px 0;
}

.site-container .rm-player .audio-share ul li:last-child {
	border-bottom: none;
}

.site-container .rm-player .audio-share ul li span {
	color: #aaa;
	display: inline-block;
	font-size: 12px;
	font-weight: bold;
	letter-spacing: 2px;
	text-transform: uppercase;
	width: 15%;
}

.site-container .rm-player .audio-share ul li input[type=text] {
	cursor: text;
	padding: 5px;
	margin: 0 5% 0 0;
	width: 75%;
}

.site-container .rm-player .audio-share .share-player-share {
	display: inline-block;
	height: 22px;
	margin: 0 5px;
	padding: 0;
	position: relative;
	top: 5px;
	width: 75%;
}

.site-container .rm-podcast footer {
	margin-bottom: 25px;
}

.site-container .mejs-container {
    background: none;
    min-height: 50px;
    margin-bottom: 0;
}

.site-container .rm-player-controls > .mejs-container {
	overflow: hidden;
    width: 90% !important;
}

.site-container .mejs-container .mejs-controls,
.site-container .mejs-container .mejs-inner {
    overflow: hidden;
    width: 100%;
}

.site-container .mejs-container .mejs-controls {
    background: #f5f5f5;
    color: #333;
    height: 50px !important;
}

.site-container .mejs-container .mejs-controls .mejs-play,
.site-container .mejs-container .mejs-controls .mejs-pause,
.site-container .mejs-controls .mejs-volume-button {
	border: none !important;
    height: 50px;
    width: 45px;
}

.site-container .mejs-controls .mejs-volume-button,
.site-container .mejs-controls .mejs-fullscreen-button{
	width: 30px;
}

.site-container .mejs-container .mejs-controls .mejs-play button,
.site-container .mejs-container .mejs-controls .mejs-pause button,
.site-container .mejs-controls .mejs-volume-button button,
.site-container .mejs-controls .mejs-fullscreen-button button { 
	background-image: url(../images/player-icons.png);
	background-position: 0px 0px;
	background-size: 130px 71px;
	border: none !important;
	margin: 8px;
	height: 34px;
	opacity: 0.7;
	width: 34px;

	box-shadow: none;
	-moz-box-shadow: none;
	-webkit-box-shadow: none;
	
    -webkit-transition: opacity 0.5s ease-in-out;
	-moz-transition:    opacity 0.5s ease-in-out;
	-ms-transition:     opacity 0.5s ease-in-out;
	-o-transition:      opacity 0.5s ease-in-out;
	transition:         opacity 0.5s ease-in-out;
}

.site-container .mejs-container .mejs-controls .mejs-pause button {
	background-position: -37px 0px;
}

.site-container .mejs-controls .mejs-volume-button button {
	background-position: -71px 0px;
	height: 30px;
	margin: 9px 2px;
	width: 28px;
}

.site-container .mejs-controls .mejs-fullscreen-button button {
	background-position: -100px 0px;
	height: 30px;
	margin: 9px 0px;
	width: 28px;
}

.site-container .mejs-container .mejs-controls .mejs-play button:hover,
.site-container .mejs-container .mejs-controls .mejs-pause button:hover,
.site-container .mejs-controls .mejs-volume-button button:hover,
.site-container .mejs-controls .mejs-fullscreen-button button:hover { 
	opacity: 1;
}

.site-container .mejs-controls .mejs-volume-button.mejs-unmute button {
	opacity: 0.3;
}

.site-container .mejs-controls .mejs-button button:focus {
	outline: none !important;
}

.site-container .mejs-container .mejs-controls .mejs-time {
    height: 50px;
    line-height: 50px;
    padding: 0;
    text-align: center;
    width: 60px;
}

.site-container .mejs-container .mejs-controls .mejs-time span {
    color: #aaa;
    float: none;
    font-size: 13px;
    line-height: 53px;
    margin-right: 0;
    text-align: center;
}

.site-container .mejs-controls div.mejs-time-rail {
    height: 50px;
    padding: 0;
}

.site-container .mejs-controls .mejs-time-rail .mejs-time-total,
.site-container .mejs-controls .mejs-time-rail .mejs-time-loaded,
.site-container .mejs-controls .mejs-time-rail .mejs-time-current,
.site-container .mejs-controls .mejs-horizontal-volume-slider .mejs-horizontal-volume-total,
.site-container .mejs-controls .mejs-horizontal-volume-slider .mejs-horizontal-volume-current {
    border-radius: 10px;
    height: 7px;
}

.site-container .mejs-controls .mejs-time-rail .mejs-time-total {
    background: #ccc;
    margin-top: 23px;
    line-height: 50px;
}

.site-container .mejs-controls .mejs-horizontal-volume-slider .mejs-horizontal-volume-total {
	background: #ccc;
	margin-top: 12px;
}

.site-container .mejs-controls div.mejs-horizontal-volume-slider {
    height: 50px;
    overflow: hidden;
}

.site-container .mejs-controls .mejs-time-rail .mejs-time-loaded {
    background: #fff;
}

.site-container .mejs-controls .mejs-time-rail .mejs-time-current {
    background: #333;
    position: relative;
	
    -webkit-transition: all 0.5s ease-in-out;
	-moz-transition:    all 0.5s ease-in-out;
	-ms-transition:     all 0.5s ease-in-out;
	-o-transition:      all 0.5s ease-in-out;
	transition:         all 0.5s ease-in-out;
}

.site-container .mejs-controls .mejs-horizontal-volume-slider .mejs-horizontal-volume-current {
	background: #333;
	margin-top: 12px;
}

.site-container .mejs-controls .mejs-time-rail .mejs-time-current:after {
    background: #333;
    border-radius: 50%;
    display: block;
    content: "";
    position: absolute;
    right: -8px;
    top: -2px;
    height: 11px;
    width: 11px;
    z-index: 999;
}

.site-container .mejs-controls .mejs-time-rail .mejs-time-float {
    background: none;
    border: none;
    color: #aaa;
    top: -35px;
}

.site-container .mejs-controls .mejs-time-rail .mejs-time-float-current {
    margin: 0;
}

.site-container .mejs-controls .mejs-time-rail .mejs-time-float-corner {
    display: none;
}

.rm-podcast .buttons {
	margin-bottom: 30px;
}

.rm-podcast .buttons .button {
	margin-right: 10px;
}

.rm-podcast .buttons .button span {
	font-size: 16px;
	margin-right: 15px;
	line-height: 1.5;
}

.sidebar .rm-player .rm-player-image,
.sidebar .rm-player .mejs-container .mejs-time-rail,
.sidebar .rm-player .mejs-container .mejs-duration-container {
	display: none;
}

.sidebar .rm-player-controls > .mejs-container {
	width: 75% !important;
}

.sidebar .rm-player .share-button {
	width: 25% !important;
}

.sidebar .rm-player .audio-share ul li span,
.sidebar .rm-player .audio-share ul li input[type=text],
.sidebar .rm-player .audio-share .share-player-share {
	float: none;
	width: 100%;
}

.site-container .rm-player .audio-share {
	padding: 0;
}

.site-container .rm-player .audio-share ul li {
	padding: 5px 10px;
}

.site-container .rm-player .audio-share ul li span {
	font-size: 10px;
	width: 17%;
}

.site-container .rm-player .audio-share ul li input[type=text] {
	margin: 0;
	width: 60%;
}

.podcast-player-embed .site-container .rm-player .audio-title {
	min-height: 90px;
}