calendar.css

.DayPicker {
  background: #28262e;
  border-radius: 10px;
}

.DayPicker-wrapper {
  padding-bottom: 0;
}

.DayPicker,
.DayPicker-Month {
  width: 100%;
}

.DayPicker-Month {
  border-collapse: separate;
  border-spacing: 8px;
  margin: 16px;
}

.DayPicker-Day {
  width: 40px;
  height: 40px;
}

.DayPicker-Day--available:not(.DayPicker-Day--outside) {
  background: #3e3b47;
  border-radius: 10px;
  color: #fff;
}

.DayPicker:not(.DayPicker--interactionDisabled)
  .DayPicker-Day:not(.DayPicker-Day--disabled):not(.DayPicker-Day--selected):not(.DayPicker-Day--outside):hover {
  background: ${shade(0.2, '#3e3b47')};
}

.DayPicker-Day--today {
  font-weight: normal;
}

.DayPicker-Day--disabled {
  color: #666360 !important;
  background: transparent !important;
}

.DayPicker-Day--selected {
  background: #ff9000 !important;
  border-radius: 10px;
  color: #232129 !important;
}

Muito legal pessoal, parabéns pelo trampo