mobile-config-firefox/chrome/floating_findbar_on_top.css

/* Source file https://github.com/MrOtherGuy/firefox-csshacks/tree/master/chrome/floating_findbar_on_top.css made available under Mozilla Public License v. 2.0
See the above repository for updates as well as full license text. */

/* This style makes findbar appear as floating box at the top-left of the content area.
 * If you want the findbar on right side instead then create a new pref
 * userchrome.floating-findbar-on-right.enabled and set it to true and restart Firefox
 * 
 * Note that privacy.resistFingerprinting.letterboxing prevents this from working properly
 */

findbar{
  -moz-box-ordinal-group: 0; /* Fx <112 compatibility */
  order: -1;
  margin-bottom: -33px;
  position: relative;
  border-top: none !important;
  padding: 0 !important;
  transition: transform 82ms linear, opacity 82ms linear 32ms !important;
  background: none !important;
  pointer-events: none;
  z-index: 1;
  white-space: nowrap;
}

.findbar-container > .findbar-find-fast{
  padding: var(--toolbarbutton-inner-padding) 1px;
  margin: 0 !important;
}

findbar[hidden]{ transform: translateY(-30px);}

findbar > .findbar-container,
findbar > .close-icon{
  border: 1px solid var(--chrome-content-separator-color);
  border-width: 0 0 1px 0px;
  background: var(--uc-light-bkgnd-color,var(--toolbar-bgcolor)) !important;
  pointer-events: auto;
}

findbar > .findbar-container{
  border-bottom-right-radius: 4px;
  border-right-width: 1px;
  height: initial !important;
  margin-inline: 0px !important;
  overflow-inline: visible !important;
}

.findbar-find-status{
  display: flex;
  overflow: hidden;
  text-overflow: ellipsis;
  -moz-box-flex: 1; /* Fx <112 compatibility */
  flex-grow: 1;
}
 
.findbar-closebutton{
  margin: 0 !important;
  border-radius: 0 !important;
  padding: 5px !important;
  width: initial !important;
  -moz-box-ordinal-group: 0; /* Fx <112 compatibility */
  order: -1;
}
.findbar-closebutton > image{ padding: 3px }
.findbar-closebutton:hover > image{
  background: var(--toolbarbutton-hover-background) !important;
  border-radius: 4px
}
findbar > .findbar-container > hbox{ margin: 0 5px }
 
findbar::after{
  content:"";
  display: flex;
  -moz-box-flex: 100; /* Fx <112 compatibility */
  flex-grow: 100;
} 

@supports -moz-bool-pref("userchrome.floating-findbar-on-right.enabled"){
  findbar{
    -moz-box-direction: reverse; /* Fx <112 compatibility */
    flex-direction: row-reverse;
  }
  findbar > .findbar-container{
    -moz-box-direction: reverse;
    flex-direction: row-reverse;
    border-inline-width: 1px 0px;
    border-bottom-right-radius: 0px;
    border-bottom-left-radius: 4px;
  }
  /*
  Move findbar so it isn't over the scrollbar
  Delete if you want findbar to begin from right window edge
  */
  findbar{
    margin-right: 16px;
    border-right: 1px solid var(--chrome-content-separator-color);
  }
}