div.jumbotron {
  background-image: url(../img/arithmetic_back.jpg);
  background-repeat: no-repeat;
  background-position: left center;
}

p {
  line-height: 2rem;
}

blockquote {
  margin-left: 2rem;
  margin-right: 2rem;
}

strong {
  color: #ff0000;
}

/* 公式 */
.formula {
  border: 1px ridge #cccccc;
  border-collapse: separate;
  text-align: center;
  padding: 1rem;
  margin-top: 1rem;
  margin-bottom: 1rem;
}
.formula td {
  vertical-align: text-top;
}
.formula .expression {
  font-size: 2rem;
  font-weight: bold;
}
.formula .expression-text {
  font-size: 1.6rem;
  font-weight: bold;
}
.formula .expression-text td {
  vertical-align: middle;
}
.formula-green {
  color: #548235;
}
.formula-blue {
  color: #2f75b5;
}
.formula-red {
  color: #ff0000;
}
.formula-pink {
  color: #ff00ff;
}

.next-page {

}