Update Calendar styling snippet

[glebfox]

Environment

• Documentation version: 7.0+
• Part of the documentation: Manual
• Existing page: https://doc.cuba-platform.com/manual-latest/gui_Calendar.html

Description of the bug or enhancement

Current styles example is applicable only for Monthly view all-day events and doesn't correspond to the screenshot

.v-calendar-event.event-green {
  background-color: #c8f4c9;
  color: #00e026;
}

The correct styles are:

.v-calendar-week-wrapper .v-calendar-event-event-green {
  color: #037516;

  .v-calendar-event-content {
    background-color: #c8f4c9;
  }
}

Pay attention that these styles apply only to the Week/Day view events and correspond to the screenshot in the doc.