gnome-shell-dark-theme/gnome-shell-sass/widgets/_search-entry.scss

// Search entry
.search-entry {
  border-radius: $forced_circular_radius;
  margin-top: $base_padding * 2;
  margin-bottom: $base_padding;
  width: 24em;

  @extend %system_entry;

  .search-entry-icon {
    icon-size: $scalable_icon_size;
    margin-top: 2px; // center vertically
    padding: 0 $base_margin;
  }
}