body {
  width: 100%; /*ページ全体の幅は100%と指定する*/
  text-align: center; /*ページ全体を中央揃えにする*/
}

h1 {
  font-size: 1.5em;
  font-weight: bold;
  margin: 15px 0;
}

a {
  color: skyblue;
}

.main-container {
  width: 100%;
  margin: 100px auto;
}

.container {
  position: relative;
  width: 70%;
  padding-bottom: 38.25%; /* 16:9アスペクト比 (9 / 16 * 100) */
  margin: 0 auto;
  overflow: hidden;
  border:solid 3px #000;
}

.inner {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  display: grid; /* Gridを使用 */
  justify-items: center; /* 水平方向の中央揃え */
  align-items: center; /* 垂直方向の中央揃え */
}

.content {
  width: 100%;
  height: 30px;
  box-sizing: border-box;
  font-size:40px;
}

@media screen and (max-width: 600px) {
  .content {
    font-size:20px;
  }
}

#question-area {
  height:140px;
}

#answer-area {
  width: 60%;
  padding: 10px;
  border-radius: 2px;
  border: 1px solid #000;
  appearance: none;
  -webkit-appearance: none;
  -moz-appearance: none;
  max-width: 250px;
  margin-top:20px;
  margin-bottom:10px;
}

.btn-square {
  display: inline-block;
  padding: 20px 40px;
  text-decoration: none;
  background-color: #333;
  color: #FFF;
  border-bottom: solid 4px #222;
  border-radius: 10px;
}
.btn-square:active {
  -webkit-transform: translateY(4px);
  transform: translateY(4px);
  border-bottom: none;
}


.btn-blue {
  background-color: hsl(194, 96%, 47%);
  color: #FFF;
  border-bottom: solid 4px #0073b6;
}

#retry-btn {
  display: inline-block;
  padding: 20px 40px;
  text-decoration: none;
  background-color: #860000;
  color: #FFF;
  border-bottom: solid 4px #6b0000;
  border-radius: 10px;
  font-size: 20px;
}
#retry-btn:active {
  -webkit-transform: translateY(4px);
  transform: translateY(4px);
  border-bottom: none;
}

#x-mark-area {
  display:block;
  width:100%;
  font-size: 35vw;
}

@media screen and (max-width: 600px) {
  #x-mark-area {
    font-size: 90vw;
  }

}

#cross-mark-container {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  background-color: rgba(0, 0, 0, 0.9);
  color: #ff0000;
  z-index: -1;
  opacity: 0;
}

@keyframes fadeIn {
  0% {
      opacity: 0;
  }
  100% {
      opacity: 1;
  }
}

.fade-in {
  animation: fadeIn 0.5s forwards;
}

.alert-area {
  margin-top:20px;
  color:red;
  margin-bottom:20px;
}

#hint-area {
  z-index: 999;
  margin-top: 100px;
}