app.css

/* Our CSS. I'm afraid I didn't have a great deal of time to spend ordering and structuing the CSS in an attractive or particularly semantic way. I think it's reasonably clean and obvious though. */

body {
  font-family: georgia, serif;
  font-size: 0.9em;
}

/* It's responsive up to a point, and then it's fixed. Does 700 seem about right? */
#app {
  max-width: 700px;
}

#auth {
  margin-left: 8px;
}

[type=radio] {
  position: absolute;
  clip: rect(0, 0, 0, 0);
}

li {
  padding: 8px 8px 8px 0;
  border-bottom: 2px solid rgb(246, 244, 239);
}

li a {
  color: #333;
  text-decoration: none;
}

*, *:before, *:after {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
   
.main {
  margin: 0 auto;
  min-width: 320px;
  max-width: 800px;
}

.content {
  background: #fff;
  color: #373737;
}

.content > div {
  display: none;
  padding: 8px 25px 5px;
}
 
input(not:#key) {
  display: none;
}

label {
  display: inline-block;
  padding: 6px 25px;
  font-weight: 600;
  text-align: center;
}

.options {
  background: black;
  margin-bottom: 2px;
  color: white;
  padding: 8px
}

.options label {
  padding: 4px;
  font-family: sans-serif;
  font-weight: bold;
}

input[type=radio] + label {
  background: rgb(229, 228, 223);
  cursor: pointer;
  margin-right: 2px
}

input[type=radio]:checked + label {
  background: #fff;
  cursor: default;
}

#tab0:checked ~ .content #content0,
#tab1:checked ~ .content #content1,
#tab2:checked ~ .content #content2 {
  display: block;
}

h1, #instructions {
  width: 280px;
  margin-top: 20px;
}

h1 {
  margin-bottom: 16px
}

#go, #key {
  padding: 8px;
  font-size: 1.1em;
}