I was recently working on a project that used the date filter feature in Bricks. Unfortunately, as Bricks tends to do, the font size was ridiculously small, and the opacity levels of the font made it almost unreadable.

Here is the CSS I used to fix the issue.

.flatpickr-calendar * {
    color: black !important;
    font-size: 1.05em;
    font-weight: 600!important;
}
.flatpickr-month select *{
  color: black !important;
   font-weight: 600;
}
.prevMonthDay,.nextMonthDay{
  color: #00000080 !important;
}
.flatpickr-weekday{
  font-size: 12px!important;
}

Here is a before-and-after screenshot:

I am still researching another bug that has the date picker panel completely off the screen on wide widths.