.accordion-item {
    display: none;
}

.accordion-button::after{
   content: ">"; 
   display: inline-block;
   /* 左右余白用マージン　 */
   margin: 0 1em;
   transform: rotate(90deg);
   transition: ease .3s;
}

.accordion-button.open::after{
    transform: rotate(-90deg);
 }