Hatch homepage : center title on articles

Hi,

I made a child theme from the Hatch theme, have a look here : https://kissnvroom.com/

I’m trying desperately to center the post title on the thumbnails on the homepage. The idea would be to center the title, and have the semi-transparent background fitting with the text. The maximum width / height of the white background should be the height/width of the thumbnails minus 5 pixels (for example).

Is someone good enough with CSS in order to help me deal with this ?

thanks a lot!