How to change Feature widget title text from h5 to h3?

Hi,

For SEO reasons, I would like the title text in the Features widgets I installed on my homepage to be h3 tags instead of h5.
I found thread explaining how to modify h1, h2…. styles, but not how to modify the widget itself.
I’m looking for a CSS solution (have installed the Custom CSS plugin).

To be clear, I am referring to the following bits of text (see page www.recolte.ca):
– Consultation
– Formation
– Mobilisation

and then
– Parler la bouche pleine
– Laboratoire alimentaire
– Recherche collaborative

Thanks a lot!
Marina