How to translate Calendar Day

If you want to translate Calendar Day, from this
MO >> MON
TU >> TUE
WE >> WED
…

You can use this code to Custom CSS box

th.yui3-calendar-weekday {
    visibility: hidden;
}
th.yui3-calendar-weekday:before {
    visibility: visible;
}
th.yui3-calendar-weekday[aria-label="Sunday"]:before {
    content: "SUN";
}
th.yui3-calendar-weekday[aria-label="Monday"]:before {
    content: "MON";
}
th.yui3-calendar-weekday[aria-label="Tuesday"]:before {
    content: "TUE";
}
th.yui3-calendar-weekday[aria-label="Wednesday"]:before {
    content: "WED";
}
th.yui3-calendar-weekday[aria-label="Thursday"]:before {
    content: "THU";
}
th.yui3-calendar-weekday[aria-label="Friday"]:before {
    content: "FRI";
}
th.yui3-calendar-weekday[aria-label="Saturday"]:before {
    content: "SAT";
}

Result