<label for="camp-week">Choose a week in May or June:</label>

<input type="week" name="week" id="camp-week" min="2018-W18" max="2018-W26" required />

label {
  display: block;
  font:
    1rem 'Fira Sans',
    sans-serif;
}

input,
label {
  margin: 0.4rem 0;
}