jn-customizer-ui-styles.css

/* re-skin the title sections */
#customize-theme-controls li.accordion-sectional-title {
  display: block !important;
  background: none;
  outline: none;
  padding: 25px 15px 10px 15px;
  border: none;
}
#customize-theme-controls li.accordion-sectional-title h3 {
  font-size: 18px;
  line-height: 1.6;
  font-weight: 400;
  padding: 0;
  margin: 0;
  outline: none;
  color: #2d3136 !important; /* no visual hover effects */
  border: none !important; /* no visual hover effects */
  background: none !important; /* no visual hover effects */
}
/* hide the title arrow */
#customize-theme-controls li.accordion-sectional-title h3:after {
  display: none;
}
/* style the description */
span.sectional-title-description {
    margin-top: 5px;
    display: block;
    font-style: italic;
}
/* if title is first in custmiser panel, remove top border */
#customize-theme-controls li.accordion-sectional-title:nth-child(2) {
  border-top: none;
  padding-top: 15px;
}
#customize-theme-controls li.accordion-sectional-title + li.accordion-section {
  border-top: 1px solid #ddd;
}