<section>
  <table>
    <tr>
      <td>a</td>
      <td>b</td>
      <td>c</td>
      <td>d</td>
      <td>e</td>
    </tr>
    <tr>
      <td>f</td>
      <td>g</td>
      <td>h</td>
      <td>i</td>
      <td>j</td>
    </tr>
    <tr>
      <td>k</td>
      <td>l</td>
      <td>m</td>
      <td>n</td>
      <td>o</td>
    </tr>
    <tr>
      <td>p</td>
      <td>q</td>
      <td>r</td>
      <td>s</td>
      <td>t</td>
    </tr>
    <tr>
      <td>u</td>
      <td>v</td>
      <td>w</td>
      <td>x</td>
      <td>y</td>
    </tr>
  </table>
</section>

body {
  background: #33405F;
  font-family: 'Open Sans', sans-serif;
  font-size: 16px;
}

section {
  background: #EEEEEE;
  border-radius: 3px;
  box-shadow: 1px 2px 10px rgba(0, 0, 0, 0.5);
  margin: 1em auto;
  max-width: 232px;
  padding: 1em;
}

table {
  width: 200px;
  margin: 0 auto 1em;
  border-collapse: collapse;
}

td {
  position: relative;
  background: #DDDDDD;
  border: 2px solid #FFFFFF;
  color: #232C88;
  cursor: pointer;
  padding: 5px 0;
  text-align: center;
  text-transform: uppercase;
  transition: background 0.2s ease-in-out, color 0.2s ease-in-out;
  width: 20%;

  &::before {
    position: absolute;
    top: -2px;
    right: -2px;
    bottom: -2px;
    left: -2px;
    border: 2px solid #232C88;
    content: '';
    opacity: 0;
    transition: opacity 0.2s;
    width: auto;
    height: auto;
  }

  &:hover {
    background: #FFFFFF;
    color: darken(#232C88, 5%);
  }

  &:hover::before {
    opacity: 1;
  }
}