h1 {
  text-align: center;
}
h2 {
  margin-left: 200px;
}
h3 {
  margin-left: 0px;
}

.plink {
  text-decoration:underline;
}
input  {
  width: 6em;
}
select {
  width: 6em;
}

.oa_text {
  font-size: large;
  margin: 0px 200px 50px 200px;
  background: lightgrey;
  border: thin solid;
  padding: 20px;
}

.equation {
  margin-left: 3em;
  font-family: courier;
  font-size: medium;
  margin-top: 20px;
  margin-bottom: 20px;
}

.subtable {
  text-align: center;
  border: thin solid;
  border-collapse: collapse;
}

.subtable td {
  border: thin solid;
  margin: 6px;
}

.subtable tr {
  border: thin solid;
}

.op_img {
  border: thin solid;
  margin: 6px;
}