Four Card Feature(html, css)

I think the main difficulties I found with this was simply fitting each panel more than anything- just the tedium mostly. One thing I'm still unsure about is the size of the text above it in the center. But other than that- would it be better to use something like flexbox with this? I still haven't really familiarized all too much with flexbox, so I don't know, is that simply a design technique using CSS, or is it a library or something? Anyway, feel free to give me feedback and suggestions!