Template:BiomeSpawnEntry/styles.css

/* Remove all padding on the <td class="biomespawn-cell"> itself */
td.biomespawn-cell {
  padding: 0 !important;
}

/* Remove any paragraph margins/​padding that the wiki parser might inject */
td.biomespawn-cell > p {
  margin: 0 !important;
  padding: 0 !important;
  line-height: 1; /* optional, if you want to tighten any extra line spacing */
}

/* If there are other wrapper elements (e.g. <div>), zero them too */
td.biomespawn-cell > * {
  margin: 0 !important;
  padding: 0 !important;
}