/* 日曜日：赤 */
.flatpickr-calendar .flatpickr-innerContainer .flatpickr-weekdays .flatpickr-weekday:nth-child(7n + 1),
.flatpickr-calendar .flatpickr-innerContainer .flatpickr-days .flatpickr-day:not(.flatpickr-disabled):not(.prevMonthDay):not(.nextMonthDay):nth-child(7n + 1) {
    color: red;
}
 
/* 土曜日：青 */
.flatpickr-calendar .flatpickr-innerContainer .flatpickr-weekdays .flatpickr-weekday:nth-child(7),
.flatpickr-calendar .flatpickr-innerContainer .flatpickr-days .flatpickr-day:not(.flatpickr-disabled):not(.prevMonthDay):not(.nextMonthDay):nth-child(7n) {
    color: blue;
}