WhiteSur-gtk-theme/src/sass/gnome-shell/widgets/_keyboard.scss

// On-screen Keyboard
.word-suggestions {
  font-size: 14pt;
  spacing: 12px;
  min-height: 20pt;
}

#keyboard {
  background-color: rgba(black, 0.25);
  box-shadow: none;

  .page-indicator {
    padding: 6px;

    .page-indicator-icon {
      width: 8px;
      height: 8px;
    }
  }
}

// the container for individual keys
.key-container,
.keyboard-layout {
  padding: 4px;
  spacing: 4px;
}

//  .keyboard-row { spacing: 15px; }

.keyboard-key {
  min-height: 1.2em;
  min-width: 1.2em;
  font-weight: bold;
  font-size: round(16) + pt;
  border-radius: $mn_radius;
  border: none;
  color: $alt_fg_color;
  background-color: $solid_bg_color;
  box-shadow: 0 1px 3px rgba(black, 0.15);

  &:focus, &:hover { color: $fg_color; background-color: if($variant == 'light', white, lighten($solid_bg_color, 10%)); }
  &:checked, &:active { color: $fg_color; background-color: darken($solid_bg_color, 10%); }
  &:grayed { //FIXME
    background-color: $alt_dark_bg_color;
    color: $light_alt_fg_color;
    border-color: $alt_dark_bg_color;
  }

  &.default-key { // non-character keys
    background-color: $alt_solid_bg_color;
    box-shadow: 0 2px 3px rgba(black, 0.15);

    &:focus, &:hover { color: $fg_color; background-color: lighten($alt_solid_bg_color, 10%); }
    &:checked, &:active { color: $fg_color; background-color: darken($alt_solid_bg_color, 10%); }
  }

  &.enter-key { // enter key is suggested-action
    color: $light_fg_color;
    background-color: $primary_color;
    box-shadow: 0 2px 3px rgba(black, 0.15);

    &:focus, &:hover { color: $light_fg_color; background-color: lighten($primary_color, 5%); }
    &:checked, &:active { color: $light_fg_color; background-color: darken($primary_color, 10%); }
  }

  &.shift-key-uppercase {
    &, &:focus, &:hover, &:checked, &:active {
      color: $primary_color;
    }
  }

  StIcon { icon-size: 1.125em; }
}

.keyboard-subkeys { //long press on a key popup
  color: inherit;
  -arrow-border-radius: $bt_radius;
  -arrow-background-color: rgba(black, 0.45);
  -arrow-border-width: 0;
  -arrow-border-color: transparent;
  -arrow-base: 20px;
  -arrow-rise: 10px;
  -boxpointer-gap: 5px;
  box-shadow: 0 2px 5px rgba(black, 0.25);
}