Possibility to configure size of labels

### Description

It should be possible to configure the size of a label so that it matches its intended level in the document tree.

### Additional Information

The currently used workaround for this is to use customized formatting inside the text resource. This is prone to DOM and accessibility errors, and it requires users to manually format the text the same way in all languages.

No file or test is named. Start by locating the label-rendering component and the existing configuration or styling conventions; determine how label levels are represented and how localized text is rendered. Done means label size can be configured by intended document level without per-language manual formatting or introducing DOM and accessibility problems.

Written by the indexing model from the issue text.