Open your theme.liquid file in the online code editor, go to line no 61 and add the class site-header__search-input--visible
to the search box input, like so:
<input type="search" name="q" id="SiteNavSearch" placeholder="{{ 'general.search.placeholder' | t }}" aria-label="{{ 'general.search.placeholder' | t }}" class="site-header__search-input site-header__search-input--visible">
You'll need to scroll to the right, it's a long line of code:
Followed these instructions exactly and this class change had no effect?
Looking in theme.scss.liquid there doesn't appear to be a class "site-header__search-input--visible"?