Why is my background color for my photos changing when I add the next HTML section after it?

Hey guys, I’m trying to plug away at this Portfolio project and am kind of stuck at the moment. I’m running into an issue where I’ve tried to set a background color behind my images in the portfolio section and it works just like I want it to until I try to introduce a new HTML section after it. Basically, my background color is set in CSS to rgba(16,68,136,0.7) and the alpha channel produces a lighter, more transparent look like I want it to. But as soon as I enter any new HTML after the photos, it reverses the alpha channel back to 1. I’ve tried to nest the section in it’s own div, I’ve tried to modify it further using more CSS but I can’t seem to get it to stop altering itself when I run the code. Here’s a link to my codepen page. For reference, I want the background color behind my images to be the same lighter blue color as the one with a picture of myself and my dad. I know I could probably just find a lighter blue color to replace it but I want to understand why my photo background is being modified for reasons beyond my understanding.

Use float: left; on the .photos div.

Explanation (kinda) here:

That was exactly it! Thank you so much!