trilium/src/public/stylesheets/calendar.css

.calendar-widget *, .calendar-widget *:before, .calendar-widget *:after {
  box-sizing: border-box;
}

.calendar-widget {
  margin: 0 auto;
  overflow: hidden;
  width: 100%;
}

.calendar-widget .calendar-btn {
  -moz-user-select: none;
  -ms-user-select: none;
  -webkit-appearance: button;
  background: none;
  border: 0;
  color: inherit;
  cursor: pointer;
  font-size: x-large;
  line-height: normal;
  min-width: 27px;
  outline: none;
  overflow: visible;
  padding: 0;
  text-align: center;
}

.calendar-widget .calendar-header {
  align-items: center;
  display: flex;
  padding: 0 0.5rem 0.5rem 0.5rem;
}

.calendar-widget .calendar-header__label {
  font-weight: bold;
  text-align: center;
  width: 100%;
}

.calendar-widget .calendar-week {
  display: flex;
  flex-wrap: wrap;
}

.calendar-widget .calendar-week span {
  flex-direction: column;
  flex: 0 0 14.28%;
  font-size: 1rem;
  font-weight: bold;
  max-width: 14.28%;
  padding-top: 5px;
  padding-bottom: 5px;
  text-align: center;
  text-transform: uppercase;
}

.calendar-widget .calendar-body {
  display: flex;
  flex-wrap: wrap;
}

.calendar-widget .calendar-date {
  align-items: center;
  background-color: var(--main-background-color);
  display: flex;
  flex-direction: column;
  flex: 0 0 14.28%;
  max-width: 14.28%;
  padding: 0.4rem 0;
  font-size: 120%;
}

.calendar-widget .calendar-date:hover {
  color: var(--hover-item-text-color);
  background-color: var(--hover-item-background-color);
}

.calendar-widget .calendar-date-active {
  background-color: var(--active-item-background-color);
  color: var(--active-item-text-color);
}

.calendar-widget .calendar-date-today {
  font-weight: bold;
}

.calendar-widget .calendar-date-exists {
  text-decoration: underline !important;
}

.calendar-widget .calendar-date:not(.calendar-date-active) {
  cursor: pointer;
}