Reproduction steps
1. Upgrade Jenkins version from 2.504.3 to latest 2.516.1;
2. Restart it and find the image with #jenkins-name-icon is gone;

my current script in Extra CSS inside 'manage jenkins' > appearance is like this:
#jenkins-head-icon {content:url("/html/11.png");}#jenkins-name-icon{content:url("/html/images/international/22.png");width: 750px;max-width:70%;height: auto;}

The script works well in 2.504.3 and all previous versions together with simple-theme-plugin.