* {
  box-sizing: border-box;
}

body {
  width: 50%;
  min-width: 490px;
  margin: auto;
  font-family: sans-serif;
  font-size: medium;
}

#by {
  font-size: x-small;
}

.btn {
  display: inline-block;
}

.btn > button {
  margin-top: 3px;
  margin-right: 7px;
}

.h-center {
  display: flex;
  justify-content: center;
}

form > p,
hr + p,
div + h3,
pre,
#run {
  margin-left: 5px;
}

table {
  width: 100%;
  margin-right: 0px;
}

#txtable,
#rxtable {
  width: 50%;
}

select {
  width: 100%;
}