.calendar {
  display: grid;
  grid-template-columns: repeat(7, 1fr);
  gap: 2px;
  width: 700px;
  margin: 0 auto;
}

.day {
/*
  width: 100px;
  width: calc( 100% / 7 );
  width: 100%;
  
  height: 100px;
*/

aspect-ratio: 1 / 1;

  border: 1px solid #ccc;
  box-sizing: border-box;
  position: relative;
  background-color: #f0f0f0;

  display: flex;
  justify-content: center;
  align-items: center;
  overflow: hidden;
}

.date-number {
  font-size: 56px;
  font-weight: bold;
  color: white;
  z-index: 1;
}


.calendar-header {
  display: flex;
  justify-content: center;
  align-items: center;
  font-size: 1.8em;
  font-weight: bold;
/*
  margin: 20px 0;
  gap: 30px;
*/
}

.month-nav {
  text-decoration: none;
  font-size: 1.5em;
  color: #333;
  padding: 5px 10px;
  border-radius: 5px;
}


.month-nav:hover {
  background-color: #eee;
  color: #000;
}


.weekday {
  font-weight: bold;
  font-size: 48px;
  background-color: #ddd;
  text-align: center;
  padding: 5px 0;
}


/* -------------------------------------- スマホ ------------------------------ */
@media (max-width: 768px) {


.calendar {
  width: 100%;
}


.date-number {
  font-size: 10vw;
}


.weekday {
  font-size: 10vw;
}



}