select2/pages/03.appearance/02.theming/docs.md

title	taxonomy	process	never_cache_twig
Theming	category docs	twig true	true

Theme support

Select2 supports custom themes using the theme option so you can style Select2 to match the rest of your application.

These are using the classic theme, which matches the old look of Select2.

$(".js-example-theme-single").select2({
  theme: "classic"
});

$(".js-example-theme-multiple").select2({
  theme: "classic"
});

Various display options of the Select2 component can be changed: You can access the <option> element (or <optgroup>) and any attributes on those elements using .element.

Responsive design - Percent width

Select2's width can be set to a percentage of its parent to support responsive design. The two Select2 boxes below are styled to 50% and 75% width respectively.

<select class="js-example-responsive" style="width: 50%"></select>
<select class="js-example-responsive" multiple="multiple" style="width: 75%"></select>

Select2 will do its best to resolve the percent width specified via a CSS class, but it is not always possible. The best way to ensure that Select2 is using a percent based width is to inline the style declaration into the tag.