Panel: title width is different from content width

[bpasero]

Testing: #36906

Using dev tools I notice that the title container for the panel does not have the same width as the content container for the panels. Title seems to be 1px short. I am not seeing that e.g. in the side bar.

[bpasero]

Doesn't seem to be the case when the panel is put horizontally.

Note that in the case above I had the sidebar positioned right, not sure if that makes an impact.