body{
  font-family: 'Work Sans', arial, sans-serif;
  font-size: 16px;
}
.content{
  margin: 0 auto;
  width: 780px;
  text-align: justify;
  text-justify: inter-word;
  overflow-wrap: break-word;
  hyphens: auto;
}
h1{
  font-family: 'Intel One Mono', serif;
  letter-spacing: -2px;
  border-bottom: 1px solid #aaa;
  line-height: 1.1em;
}
.topbar{
  border-bottom: 1px solid #6cf;
}
h2{
  font-family: 'Intel One Mono', serif;
  letter-spacing: -1px;
}
p{
  text-indent: 2em;
}
.number{
  color: #04a;
  font-size: 20px;
}
.notice{
  padding-top: 4px;
  padding-bottom: 4px;
  text-indent: 1em !important;
  border-left: 4px solid #04a;
  background-color: #def;
}
strong, b, th{
  font-family: 'Intel One Mono', serif;
}
table{
  border-collapse: collapse;
}
a{
color: #04a;
}
a:hover{
  background-color: #bdf;
}
a:focus{
  background-color: #9cf;
}
table.center{
  margin-left: auto;
  margin-right: auto;
}
th{
  background-color: #8cf;
  border: solid 2px black;
  text-align: center;
}
td{
  border: solid 1px #ccc;
  padding-left: 4px;
  padding-right: 4px;
}
.no-indent{
  text-indent: 0;
}
.center{
  text-align: center;
}
.larger{
  font-size: 18px;
}
.layout {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 2rem;
}
.layout3 {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr;
  gap: 1rem;
}
.layout4 {
  display: grid;
  grid-template-columns: 1fr 1fr 1fr 1fr;
  gap: 1rem;
}
#column2{
  grid-column: 2;
}
img{
  display: block;
}
.box {
  background: #bdf;
  padding: 1rem;
  position: relative;
}

.box-title {
  position: absolute;
  top: 0;
  left: 0;
  font-family: 'Intel One Mono', serif;
  background: white;
  color: #04a;
  padding: 0.25rem 0.6rem;
  font-weight: bold;
}

.box-content {
  margin-top: 2rem;
}
.eq {
  display: grid;
  grid-template-columns: max-content 1ch max-content;
  column-gap: 0.3rem;
  align-items: center;
}
.eq-wrap {
  display: flex;
  justify-content: center;
}
.left{
  text-align: right;
}
.frac {
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  vertical-align: middle;
}

.bar {
  width: 100%;
  border-top: 1px solid black;
  margin: 0.05em 0;
}

.top,
.bottom {
  line-height: 1;
}

.cancel {
  position: relative;
  display: inline-block;
  padding: 0 0.08em;
}

.cancel-line {
  position: absolute;
  left: 50%;
  top: 50%;

  width: 0.08em;
  height: 100%;

  background: #000;

  transform-origin: center;
  pointer-events: none;
}

.small {
  position: absolute;
  font-size: 0.6em;
}

.small-top {
  top: -0.9em;
  right: -0.4em;
}

.small-bottom {
  bottom: -0.9em;
  right: -0.4em;
}
/* clickable exercises */
.exercise {
  cursor: pointer;
  background: white;
  transition: background linear;
}

.exercise:hover {
  background: #e8f6ff;
}

/* dark overlay */
#overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.55);
  display: none;
  z-index: 999;
}

/* modal shell */
#modal {
  position: fixed;
  inset: 0;
  display: none;
  z-index: 1000;
  justify-content: center;
  align-items: center;
}

/* inner box */
#modal-inner {
  min-width: 320px;
  background: white;
  border: 2px solid #04a;
}

/* content area */
#modal-text {
  padding: 1rem;
  border-bottom: 1px solid #04a;
}

/* close button */
#modal-close {
  padding: 0.5rem;
  text-align: center;
  cursor: pointer;
  background: #e8f6ff;
  border-top: 1px solid #04a;
}

#modal-close:hover {
  background: #cfeeff;
}