Markup: templates/output/06-components/searchheader/searchfield.html
<form class="c-search">
<input class="c-search__input" type="text" name="searchfield" placeholder="Suchbegriff"/>
<button class="c-search__button"><svg width="24" height="24" fill="currentcolor" fill-rule="evenodd" clip-rule="evenodd"><path d="M15.853 16.56c-1.683 1.517-3.911 2.44-6.353 2.44-5.243 0-9.5-4.257-9.5-9.5s4.257-9.5 9.5-9.5 9.5 4.257 9.5 9.5c0 2.442-.923 4.67-2.44 6.353l7.44 7.44-.707.707-7.44-7.44zm-6.353-15.56c4.691 0 8.5 3.809 8.5 8.5s-3.809 8.5-8.5 8.5-8.5-3.809-8.5-8.5 3.809-8.5 8.5-8.5z"/></svg><span class="visually-hidden">Suchen</span></button>
</form>
Source:
src/scss/6-components/_searchheader.scss, line 67