* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

body {
  font-family: "SF Mono", "Monaco", "Inconsolata", "Fira Mono", "Courier New", monospace;
  font-size: 14px;
  line-height: 1.6;
  max-width: 640px;
  margin: 0 auto;
  padding: 2rem 1rem;
}

a {
  color: inherit;
}

a:hover {
  opacity: 0.5;
}

h1, h2, h3 {
  font-weight: normal;
  margin: 1rem 0;
}

h1 { font-size: 1.25rem; }
h2 { font-size: 1rem; }
h3 { font-size: 1rem; }

p {
  margin: 0.5rem 0;
}

hr {
  border: none;
  border-top: 1px solid #000;
  margin: 1.5rem 0;
}

nav {
  display: flex;
  justify-content: space-between;
  margin-bottom: 2rem;
}

nav a {
  margin-left: 1rem;
}

input, button, select, textarea {
  font: inherit;
}

input[type="text"],
input[type="email"],
input[type="password"],
input[type="file"],
textarea {
  border: 1px solid #000;
  padding: 0.5rem;
  width: 100%;
  margin: 0.25rem 0 0.75rem 0;
  background: #fff;
}

input[type="checkbox"] {
  margin-right: 0.5rem;
}

button {
  background: #fff;
  color: #000;
  padding: 0.5rem 1rem;
  border: 1px solid #000;
  cursor: pointer;
}

button:hover {
  background: #000;
  color: #fff;
}

button:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

label {
  display: block;
}

.hidden {
  display: none;
}

.error {
  border: 1px solid #000;
  padding: 0.5rem;
  margin-bottom: 1rem;
}

section {
  margin: 2rem 0;
}

footer {
  margin-top: 3rem;
  padding-top: 1rem;
  border-top: 1px solid #000;
}