Issue with horizontal lines alignment between blocks

Site URL: https://frencholistic.com

I'm creating a header for a category of my blog posts (it means that I will use it as a template for future posts) with a sort of table. When I'm in the edit mode, everything looks almost fine (almost because it seems that the three horizontal block lines cannot align 'perfectly'), but as soon as I save, the three lines do not align anymore. Does someone know how to get around this?