Custom Icon for Custom Field Widget

style.css

#jmfe_widget-2 > h1:before { /* Replace the ID (jmfe_widget-2) with the widget ID from Step 1 */
    content: '\f35b'; /* replace the content here with the icon you would like to use.*/
    display: inline-block;
    font-family: Ionicons;
    speak: none;
    font-style: normal;
    font-weight: 400;
    font-variant: normal;
    text-transform: none;
    text-rendering: auto;
    line-height: 1;
    -webkit-font-smoothing: antialiased;
}