sectionを水平線で区切る
Firefoxで使えるように、
border を border-top に変えてあるstyle.css.app:not(.presentation) .line.section-title:not(.line-title) {
position: relative;
}
.app:not(.presentation) .line.section-title:not(.line-title) .text {
padding-top: 1em;
}
.app:not(.presentation) .line.section-title:not(.line-title):before {
content: "";
display: block;
width: 111%;
position: absolute;
left: -49px;
border-top: 1px lightgray solid;
}