Just want to add that I recently upgraded search_api_solr and was prompted to deploy the new config.zip. Two difficuilties I encountered were:
1. I couldn't find the "Download config.zip" button as seen when you deploy a new server. Eventually I resorted to adding a new search server. However... I found it later under the Operations dropdown menu.
2. How to deploy config.zip is confusing and I found the simplest way to do it for a self-hosted Solr server, running on Debian, was to simply stop the solr.service and copy the extracted files into /var/solr/data/{core-name}/conf/ dir, after making a backup.
Click on the field and then in "Style Settings", check "Customize label HTML", then check "Create a class".
Name it appropriately, and add the width: setting to an appropriate CSS file.