/* Comfortable layout for Kindle content manager */
@namespace url("http://www.w3.org/1999/xhtml");

@-moz-document
  url-prefix("https://www.amazon.co.jp/hz/mycd/myx"),
  url-prefix("https://www.amazon.co.jp/mn/dcw/myx")
{
  /* Add more height to "List of collection" box in "Add to collection" screen */
  .bulkAddToCollectionDialog_myx .myx-lgtbox-collection-vertical-scroll.recentCollection_myx {
    height: 35vh !important;
  }

  /* Enlarge the count of contents */
  .contentCount_myx {
    font: 1.2rem/2 sans-serif !important;
    word-spacing: 0.5em !important;
  }
  .contentCount_myx b {
    padding-right: 0.2em !important;
  }

  /* Avoid text wrap on table header */
  div[list-view-header-dmyx] .myx-column {
    white-space: nowrap !important;
    font-size: 12px !important;
  }
}

/* Comfortable layout for Kindle content manager */
@namespace url("http://www.w3.org/1999/xhtml");

@-moz-document
  url-prefix("https://www.amazon.co.jp/hz/mycd/myx"),
  url-prefix("https://www.amazon.co.jp/mn/dcw/myx")
{
  /* Add more height to "List of collection" box in "Add to collection" screen */
  .bulkAddToCollectionDialog_myx .myx-lgtbox-collection-vertical-scroll.recentCollection_myx {
    height: 35vh !important;
  }

  /* Enlarge the count of contents */
  .contentCount_myx {
    font: 1.2rem/2 sans-serif !important;
    word-spacing: 0.5em !important;
  }
  .contentCount_myx b {
    padding-right: 0.2em !important;
  }

  /* Avoid text wrap on table header */
  div[list-view-header-dmyx] .myx-column {
    color: #faa !important;
    white-space: nowrap !important;
    overflow-x: hidden !important;
    text-overflow: ellipsis !important;
  }
}

Improve visibility of header line
Improve visibility of header line
