body {
      min-width: 320px;
      margin: 0;
      color: #182a2a;
      background:
        radial-gradient(circle at 8% 8%, rgb(255 255 255 / 70%) 0, transparent 28rem),
        linear-gradient(180deg, #f6f1e8 0, #f4efe4 34rem, #eee7da 100%);
      font-family: Arial, sans-serif;
      font-size: 16px;
      line-height: 1.55;
      -webkit-font-smoothing: antialiased;
    }

    #banner {
      padding: 1em 0;
      background: #B795C0;
      color: white;
      text-align: center;
    }

    #banner h1 {
      font-size: 150%;
      margin: 0;
    }

    .nowrap {
      white-space: nowrap;
    }

    .inner {
      max-width: 800px;
      margin: auto;
      padding: 0.5em;
    }

    nav {
      padding: 0.7em 0 0;
      text-align: center;
    }

    nav a {
      display: inline-block;
      margin: 0.25em 0.65em;
    }

    main {
      max-width: 800px;
      margin: auto;
      padding: 0.5em;
      counter-reset: exercise;
    }

    h2 {
      margin: 2em 0 1em;
      padding-bottom: 0.35em;
      border-bottom: 2px solid #B795C0;
      color: #182a2a;
      font-size: 1.17em;
    }

    .intro {
      max-width: 800px;
      margin: 0 auto 1.5em;
      padding: 0.5em;
    }

    .lede {
      margin-top: 0;
    }

    table {
      display: block;
      width: 100%;
      margin: 1.2em 0 2.5em;
      border: 0;
      background: transparent;
    }

    thead {
      display: none;
    }

    tbody {
      display: block;
    }

    tbody tr {
      display: block;
      margin-bottom: 1.6em;
      border: 1px solid #d8cfd9;
      border-radius: 8px;
      overflow: hidden;
      background: rgb(255 255 255 / 72%);
      box-shadow: 0 2px 8px rgb(66 43 70 / 7%);
      counter-increment: exercise;
    }

    td {
      display: block;
      padding: 1em 1.15em;
      border: 0;
      border-bottom: 1px solid #ddd5cf;
      overflow-wrap: anywhere;
    }

    td:last-child {
      border-bottom: 0;
    }

    td:empty {
      display: none;
    }

    td::before {
      display: block;
      margin-bottom: 0.55em;
      color: #6c3483;
      font-weight: bold;
    }

    td:nth-child(1)::before {
      content: counter(exercise) ".";
      display: inline;
      margin-right: 0.35em;
      font-size: 1.08em;
    }

    td:nth-child(2)::before {
      content: "(a) Proof of statement";
    }

    td:nth-child(3)::before {
      content: "(b) Where does the proof go wrong?";
    }

    td:nth-child(4)::before {
      content: "(c) Is the statement correct? If so, give a correct proof. Otherwise, give a counterexample.";
    }

    td:nth-child(4) details {
      background: #edf5f8;
      border-left-color: #5b8196;
    }

    td:nth-child(4) details summary {
      color: #315f73;
    }


    mjx-container[display="true"] {
      max-width: 100%;
      overflow-x: auto;
      overflow-y: hidden;
    }

    .true {
      color: #2d6a4f;
      font-weight: bold;
    }

    .false {
      color: #9d3d3d;
      font-weight: bold;
    }

    .small {
      font-size: 0.92em;
    }

    details {
      margin: 0.4em 0;
      padding: 0.5em 0.7em;
      background: #f7f1f8;
      border-left: 4px solid #B795C0;
      border-radius: 0 6px 6px 0;
    }

    details summary {
      cursor: pointer;
      font-weight: bold;
      color: #6c3483;
    }

    details[open] {
      background: rgb(255 255 255 / 65%);
    }

    .fake {
      background: #f7f1f8;
      border-left-color: #B795C0;
    }

    .correct {
      background: #f1f7f2;
      border-left-color: #4d7c5b;
    }

    .warning {
      background: #fbf6e8;
      border-left-color: #c69026;
    }

    .counterexample {
      background: #fbefef;
      border-left-color: #a34a4a;
    }

    footer {
      max-width: 800px;
      margin: 2em auto 0;
      padding: 1.2em 0.5em;
      border-top: 1px solid rgb(183 149 192 / 55%);
      text-align: center;
      font-size: 0.9em;
    }

    @media screen and (max-width: 600px) {
      td {
        padding: 0.9em;
      }
    }
nav a[aria-current="page"] {
  color: #4f245f;
  font-weight: bold;
  text-decoration: none;
}

.topic-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(210px, 1fr));
  gap: 1rem;
  margin: 1.5em 0 2.5em;
}

.topic-card {
  display: flex;
  min-height: 10rem;
  padding: 1.2rem;
  border: 1px solid #d8cfd9;
  border-radius: 8px;
  background: rgb(255 255 255 / 76%);
  box-shadow: 0 2px 8px rgb(66 43 70 / 7%);
  color: #182a2a;
  flex-direction: column;
  text-decoration: none;
  transition: border-color 120ms ease, box-shadow 120ms ease, transform 120ms ease;
}

.topic-card:hover,
.topic-card:focus-visible {
  border-color: #B795C0;
  box-shadow: 0 5px 14px rgb(66 43 70 / 13%);
  transform: translateY(-2px);
}

.topic-title {
  color: #6c3483;
  font-size: 1.2rem;
  font-weight: bold;
}

.topic-count {
  margin: 0.3rem 0 0.8rem;
  color: #5b6870;
  font-size: 0.92rem;
  font-weight: bold;
}

.topic-description {
  margin: 0;
}