Example: https://jsfiddle.net/ymfq4o3r/19/

There are two elements with the same style a <button /> and a <div />.

For both elements the same css class is set. The css class defines the properties 'text-decoration: underline' and 'text-decoration-thickness: 4px'. 

In the <div /> case it works properly like expected.
In the <button /> case it does not work, but I would expect to be the same.