.QnA details[open] #arrow-minus {
    display: block;
}
.QnA details[open] #arrow-plus {
    display: none;
}

.QnA details:not([open]) #arrow-minus {
    display: none;
}
.QnA details:not([open]) #arrow-plus {
    display: block;
}

.QnA details summary::marker {
    content: '';
}

 details[open] #arrow-minus {
    display: block;
}
 details[open] #arrow-plus {
    display: none;
}

 details:not([open]) #arrow-minus {
    display: none;
}
 details:not([open]) #arrow-plus {
    display: block;
}