Template:LocaleDate/styles.css

:root { /* these variables are here to be changed by JavaScript code in MediaWiki:Common.js */
  /*--month-order:1;*/ /* TemplateStyles does not support CSS variables :-( Would need TemplateStylesExtender too */
  /*--day-order:2;*/
}

/* Setup for date flexbox */
.date-wrapper {
  align-items: baseline;
  background: #f00;
  display: inline-flex;
}
.date-year,
.date-month,
.date-day {
  display: inline-block;
}

/* Set date display order */
.date-day    { order: 1; } /* order should be set to val(--day-order) */
.date-month  { order: 2; } /* order should be set to val(--month-order) */
.date-year   { order: 3; }

/* Display dates based on "val" custom attribute in HTML */
.date-year::after,
.date-month::after,
.date-day::after {
  content: attr(val);
}

/* Add separators */
.date-year::before { content: ", "; }
.date-month::before { content: "★"; }
.date-day::before { content: "\00a0"; }   /* \00a0 is a non-breaking space */

/* Convert month numbers to month text */
.date-month[ val="1"]:after{ content: "January"; }
.date-month[ val="2"]:after{ content: "February"; }
.date-month[ val="3"]:after{ content: "March"; }
.date-month[ val="4"]:after{ content: "April"; }
.date-month[ val="5"]:after{ content: "May"; }
.date-month[ val="6"]:after{ content: "June"; }
.date-month[ val="7"]:after{ content: "July"; }
.date-month[ val="8"]:after{ content: "August"; }
.date-month[ val="9"]:after{ content: "September"; }
.date-month[val="10"]:after{ content: "October"; }
.date-month[val="11"]:after{ content: "November"; }
.date-month[val="12"]:after{ content: "December"; }

/* Add leading zero to days */
.date-day[val="1"]:after{ content: "01"; }
.date-day[val="2"]:after{ content: "02"; }
.date-day[val="3"]:after{ content: "03"; }
.date-day[val="4"]:after{ content: "04"; }
.date-day[val="5"]:after{ content: "05"; }
.date-day[val="6"]:after{ content: "06"; }
.date-day[val="7"]:after{ content: "07"; }
.date-day[val="8"]:after{ content: "08"; }
.date-day[val="9"]:after{ content: "09"; }

/* Display 4-digit years as 2-digit years (e.g. 1994 becomes '94) */
/* As far as I can tell, doing this fully requires 100 lines of CSS which kinda sucks */
/*.date-year[val="1990"]:after{ content: "'90"; }
.date-year[val="1991"]:after{ content: "'91"; }
.date-year[val="1992"]:after{ content: "'92"; }
.date-year[val="1993"]:after{ content: "'93"; }
.date-year[val="1994"]:after{ content: "'94"; }
.date-year[val="1995"]:after{ content: "'95"; }
.date-year[val="1996"]:after{ content: "'96"; }
.date-year[val="1997"]:after{ content: "'97"; }
.date-year[val="1998"]:after{ content: "'98"; }
.date-year[val="1999"]:after{ content: "'99"; }*/