gnome-shell/data/theme/gnome-shell-sass/widgets/_ibus-popup.scss

// IBus Candidate Popup
.candidate-popup-content {
  padding: 0.5em;
  spacing: 0.3em;
}

.candidate-index {
  padding: 0 0.5em 0 0;
  color: darken($fg_color,10%);
}

.candidate-box {
  padding: 0.3em 0.5em 0.3em 0.5em;
  border-radius: $base_border_radius;
  &:selected,&:hover { background-color: $selected_bg_color; color: $selected_fg_color; }
}

.candidate-page-button-box {
  height: 2em;
  .vertical & { padding-top: 0.5em; }
  .horizontal & { padding-left: 0.5em; }
}

.candidate-page-button {
  padding: 4px;
}

.candidate-page-button-previous { border-radius: $base_border_radius 0px 0px $base_border_radius; border-right-width: 0; }
.candidate-page-button-next { border-radius: 0px $base_border_radius $base_border_radius 0px;  }
.candidate-page-button-icon { icon-size: 1em; }