/* Kindle Cloud Reader tweak */
@namespace url("http://www.w3.org/1999/xhtml");

@-moz-document domain("read.amazon.co.jp") {
  /* Paging arrow */
  .pageArrow {
    background: floralwhite !important;
  }

  #kindleReader_center {
    left: 3% !important;
    right: 3% !important;
  }
  #kindleReader_pageTurnAreaLeft {
    width: 3% !important;
  }
  #kindleReader_pageTurnAreaRight {
    width: 3% !important;
    left: 97% !important;
  }

  /* Overray element opacity */
  .immersive_slide_area {
    opacity: 0.4 !important;
  }
  .immersive_slide_area:hover {
    opacity: 0.8 !important;
  }

  /* Footer height adjustment */
  #kindleReader_footer {
    height: 40px !important;
  }
  #kindleReader_footer_readerControls_left,
  #kindleReader_footer_readerControls_middle,
  #kindleReader_footer_readerControls_right {
    min-height: 40px !important;
    height: 100% !important;
  }

  #kindleReader_footer_readerControls_left,
  #kindleReader_footer_readerControls_right {
    padding-top: 8px !important;
  }

  #kindleReader_progressbar_div {
    top: 8px !important;
  }
  #kindleReader_footer_message {
    margin-top: 12px !important;
    font: 12px/1 sans-serif !important;
    letter-spacing: 0.2em !important;
    word-spacing: 1em !important;
  }
}

/* Kindle Cloud Reader tweak */
@namespace url("http://www.w3.org/1999/xhtml");

@-moz-document domain("read.amazon.co.jp") {
  /* Paging arrow */
  .pageArrow {
    background: floralwhite !important;
  }

  /* Overray element opacity */
  .immersive_slide_area {
    opacity: 0.4 !important;
  }
  .immersive_slide_area:hover {
    opacity: 0.8 !important;
  }
}

Drop the code out of use
Drop the code out of use

The parts userstyles are applied should be minimal to keep the original design as much as possible for the respect to author :)
