Reduce Font size for Product Headers, in Craft Theme

[fcojewellery]

Hi guys

Im hoping someone could help as I'm not very good with tweaking websites in css! 

I'm trying to reduce my font size across all product titles on my product pages, they're currently huge! But in my standard theme I can't make them any smaller. If I could do the same for Headers on my landing page too that would be great. '

Example : https://formationjewellery.co.uk/products/lumen-evil-eye-studs

Hoping someone can help!

Kerry