.blackboard-wrapper {
  margin: 0;
  padding: 40px 20px;
  font-family:
    -apple-system,
    BlinkMacSystemFont,
    "Helvetica Neue",
    "Yu Gothic",
    "YuGothic",
    sans-serif;
}

.blackboard-box {
  position: relative;
  box-sizing: border-box;

  max-width: 700px;
  margin: 0 auto;
  padding: 32px 36px;

  /* 黒板の基本色 */
  background-color: #202421;

  /* 黒板表面の微妙なムラ */
  background-image:
    radial-gradient(
      circle at 20% 30%,
      rgba(255, 255, 255, 0.035) 0,
      transparent 35%
    ),
    radial-gradient(
      circle at 80% 70%,
      rgba(255, 255, 255, 0.025) 0,
      transparent 30%
    ),
    linear-gradient(
      105deg,
      rgba(255, 255, 255, 0.018),
      transparent 35%,
      rgba(0, 0, 0, 0.08) 70%,
      transparent
    );

  /* 木枠 */
  border: 11px solid #8a6039;
  border-radius: 3px;

  /* 黒板内部と外側の立体感 */
  box-shadow:
    inset 0 0 20px rgba(0, 0, 0, 0.55),
    inset 0 0 2px rgba(255, 255, 255, 0.15),
    0 5px 12px rgba(0, 0, 0, 0.25);

  color: #f3f0e7;
  line-height: 1.8;
  text-align: center;
}

.blackboard-title {
  margin: 0 0 20px;
  color: #fffdf2;
  font-size: 1.7rem;
  font-weight: 600;
  letter-spacing: 0.08em;

  text-shadow:
    1px 0 rgba(255, 255, 255, 0.18),
    -1px 0 rgba(255, 255, 255, 0.08);
}

.blackboard-delivery-date {
  margin: 0 0 22px;
  color: #fff8cf;
  font-size: 1.2rem;
  font-weight: 600;
  letter-spacing: 0.04em;
  line-height: 1.5;
  white-space: nowrap;
}

.blackboard-date-number {
  display: inline-block;
  margin: 0 2px;
  font-size: 1.75em;
  font-weight: 700;
  line-height: 1;
  vertical-align: -0.08em;
}

.blackboard-separator {
  display: inline-block;
  margin: 0 14px;
  font-size: 1.1em;
}

.blackboard-notice {
  margin: 0;
  font-size: 0.95rem;
  line-height: 1.9;
  text-align: left;
}

@media (max-width: 600px) {
  .blackboard-wrapper {
    padding: 20px 8px;
  }

  .blackboard-box {
    padding: 24px 10px;
    border-width: 8px;
  }

  .blackboard-title {
    font-size: clamp(1.2rem, 5vw, 1.45rem);
  }

  .blackboard-delivery-date {
    /*
      400～500px幅でも黒板内に収まるよう、
      文字サイズを従来より小さめに設定
    */
    font-size: clamp(0.72rem, 2.65vw, 0.95rem);
    letter-spacing: -0.01em;
    white-space: nowrap;
  }

  .blackboard-date-number {
    margin: 0 1px;
    font-size: 1.55em;
  }

  .blackboard-separator {
    display: inline-block;
    margin: 0 clamp(2px, 1vw, 5px);
    font-size: 0.95em;
  }

  .blackboard-notice {
    font-size: clamp(0.78rem, 3.4vw, 0.95rem);
  }
}

@media (max-width: 400px) {
  .blackboard-wrapper {
    padding-left: 4px;
    padding-right: 4px;
  }

  .blackboard-box {
    padding-left: 6px;
    padding-right: 6px;
    border-width: 6px;
  }

  .blackboard-delivery-date {
    font-size: clamp(0.66rem, 2.9vw, 0.76rem);
    letter-spacing: -0.02em;
  }

  .blackboard-date-number {
    font-size: 1.5em;
  }

  .blackboard-separator {
    margin: 0 2px;
  }
}
@media (min-width: 770px) and (max-width: 1000px) {
  .blackboard-wrapper {
    padding: 20px 8px;
  }

  .blackboard-box {
    padding: 24px 10px;
    border-width: 7px;
  }

  .blackboard-title {
    font-size: 1.35rem;
    margin-bottom: 16px;
  }

  .blackboard-delivery-date {
    font-size: clamp(0.68rem, 1.45vw, 0.9rem);
    letter-spacing: 0;
    white-space: nowrap;
  }

  .blackboard-date-number {
    margin: 0 1px;
    font-size: 1.6em;
  }

  .blackboard-separator {
    margin: 0 clamp(2px, 0.5vw, 6px);
    font-size: 1em;
  }

  .blackboard-notice {
    font-size: 0.85rem;
    line-height: 1.8;
  }
}