jn-customizer-ui-styles.css

/* re-skin the title sections */
#customize-theme-controls li.accordion-sectional-title {
  display: block !important;
  background: none;
  outline: none;
  margin: 30px 15px 10px 15px;
}
#customize-theme-controls li.accordion-sectional-title h3 {
  font-size: 18px;
  line-height: 1.6;
  font-weight: 500;
  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;
}
#customize-theme-controls li.accordion-sectional-title + li.accordion-section {
  border-top: 1px solid #ddd;
}

/* Restyle of the standard areas */
#customize-controls li.accordion-section:not(.panel-meta) {
  margin: 0px 15px 3px;
  border: none !important;
}
#customize-controls li.accordion-section:not(.panel-meta) > h3.accordion-section-title {
  font-weight: 400;
  border: none;
  background: #f9f9f9;
  border-radius: 3px;
  padding: 10px;
  position: relative;
}
/* hover */
#customize-controls li.accordion-section:not(.panel-meta) > h3.accordion-section-title:hover {
  background: #ffffff;
}
/* focus */
#customize-controls li.accordion-section:not(.panel-meta) > h3.accordion-section-title:focus  {
  background: #ffffff;
}

/* right arrow replacement */
#customize-controls li.accordion-section:not(.panel-meta) > h3.accordion-section-title:after {
  color: #cacdd0;
  font-size: 16px;
  right: 10px;
  top: 50%;
  -webkit-transform: translateY(-50%);
  -moz-transform: translateY(-50%);
  transform: translateY(-50%);
}

/* menu hacks */
.wp-customizer .menu-item-settings {
  border: 1px solid #dddddd;
  background: #ffffff;
}
.menu-item-edit-active .menu-item-handle {
  border-color: #dddddd;
}