Add Styles to Read More Link in Your WordPress Theme - http://amethystwebsitedesign.com/add-styles-to-read-more-link-in-your-wordpress-theme/

style.css

/* Put Read more link on it's own line */
a.more-link {
	display: table;
} /* optional */

a.more-link {
	display: block;
} /* optional */

/* Remove right arrow from Twenty Twelve read more links */
a.more-link span {
	display: none;
}

/* Create a button */
a.more-link {
	background-color: #21759B;
	color: #fff;
	padding: 10px;
	text-decoration: none;
}

/* add hover style */
a.more-link:hover {
	background-color: #0F3647;
}

/* Round corners, add border */
a.more-link {
	border-radius: 3px;
	border: 1px solid #0f3647;
}

/* Add right angle quote */
a.more-link:after {
	content: "  \00BB";
  	font-size: 24px;
	vertical-align: middle;
}

/* Or use Dashicons */
a.more-link:after {
	content: " \f345";
  	display: inline-block;
  	-webkit-font-smoothing: antialiased;
  	font: normal 20px/1 'dashicons';
  	vertical-align: top;
} /* optional */

/* Line up the angle quote */
a.more-link {
	position: relative;
}

a.more-link:after {
	position: relative;
	bottom: 3px;
}