.u-center {
    display: flex;
    justify-content: center;
}
.u-center.column {
    flex-direction: column;
    justify-content: center;
}
.u-strong {
    font-weight: bold;
    color: #c61801;
    text-decoration: underline;
}
.u-margin20 {
    margin-top: 1.0em;
    margin-bottom: 1.0em;
}

.u-pagetitle {
    font-size: 4.0rem;
    padding-top: 1.0em;
}
.u-subtle {
    color: #8b9c89;
    font-size:0.8em;
}

p.u-center {
    text-align: center;
}

header {
    background-color: #2f424d;
    color: #e3eae2;
}
body {
    background-color: #fafeff;
    color: #405c62;
    font-family: "Noto Sans JP", serif;
    font-style: normal;
    font-weight: 400;
    font-size:1.8em;
}
header .u-subtle {
    color: #c0cad1;
    font-size:0.8em;
}

h1 {
    font-size: 2.5rem; padding-top: 1.0em;
    font-family: "Noto Sans JP", serif;
    font-optical-sizing: auto;
    font-weight: 500;
}
h2 {
    text-align:center;
    font-size: 2.4rem;
    padding-top: 0.5em;
    margin-bottom: 0.5em;
    position:relative;
    font-weight: 500;
    
}
h2::after {
    content: "";
    margin: 0 auto;
    display: block;
    width: 100%;
    height: 4px;
    border-radius: 2px;
    
    background: #3a536b;
}
h3 {
    font-size: 1.8rem;
    padding-top: 0.3em;
    padding-left: 0.5em;
    position:relative;
    font-weight: 400;
}
h3::before {
    content: "";
    margin: 0 auto;
    display: block;
    width:3px;
    height:1.5em;
    position:absolute;
    top:0.2em;
    left:-5px;
    background: #9dc1eb; 
}
h4 { font-size: 1.5rem; padding-top: 0.3em;}


img {
    width: 80%;
}

img.u-icon {
    max-width: 15em;
    border-radius: 100%;
    border-color: #bfeae7;
    border-width: 3px;
    border-style: solid;
    padding: 1em;
    width: 30%;
    min-width: 150px;
}

.u-footnote {
    color: rgb(173, 173, 173);
    font-size: 0.9em;
}
.u-gray {
    color: gray;
}
.u-bold {
    font-weight: bold;
}


details.custom {
  border: 2px solid #d8e0e6;
  border-radius: 10px;
  padding: 0;
  margin: 0.5em 0;
  font-family: 'Noto Sans JP', 'Kosugi Maru', sans-serif;
  box-sizing: border-box;
  transition: border 0.2s;
}

details.custom[open] {
  /* 開いたときも枠線色変えたければ */
  border-color: #a0b7c9;
}

details.custom summary {
  cursor: pointer;
  list-style: none;
  font-size: 1.25em;
  font-weight: 500;
  padding: 0.6em 1em;
  outline: none;
  user-select: none;
  display: flex;
  align-items: center;
}

details.custom summary::-webkit-details-marker {
  display: none; /* デフォルトの三角を消す */
}

details.custom summary::before {
  content: '';
  display: inline-block;
  width: 0.05em;
  height: 0.05em;
  margin-right: 0.8em;
  border-style: solid;
  border-width: 0.48em 0 0.48em 0.9em;
  border-color: transparent transparent transparent #353d4e;
  border-radius: 2px;
  transition: transform 0.3s;
  /* 少し大きめに見せる・太く */
}

details.custom[open] summary::before {
  /* 下向き▼（開いた状態） */
  transform: rotate(90deg);
}

code {
	overflow-x: scroll;
	background-color: inherit;
}