wekan/client/components/forms/datepicker.css

.datepicker-container .fields .left {
  width: 56%;
}
.datepicker-container .fields .right {
  width: 38%;
}
.datepicker-container .datepicker {
  width: 100%;
}
.datepicker-container .datepicker table {
  width: 100%;
  border: none;
  border-spacing: 0;
  border-collapse: collapse;
}
.datepicker-container .datepicker table thead {
  background: none;
}
.datepicker-container .datepicker table td,
.datepicker-container .datepicker table th {
  box-sizing: border-box;
}