Wanted jenkins give a try, installed it with

docker run --name=jenkins --publish 8080:8080 --publish 50000:50000 jenkins/jenkins:lts

(in a Vagrantfile)

After inserting the generated key by the installation the next page has the broken text layout as shown in the attached screenshot. All 3 browsers Safari, Chrome, Firefox show the broken layout.

CSS font-size: 57px and line-height: 1.4em seems related to the body font-size, not the h1 font-size, which leads to the small line-height and the garbled title text.