I just finished the National Olympiad of Informatics, and here I am hoping everything goes right. :) I spend my little free time writing this blog, about how I fixed an UI bug in Open Event Web App. I resized my browser on the desktop into the size of a phone, the navigation bar is collapsed to a small button from which menu items will be shown when it's clicked. I clicked and I noticed that: So I made a guess that the opacity of this navigation bar has been decreased. I inspected elements and tracked the name of the navigation bar. I realized that this HTML page I was reading was generated. Therefore, I looked into the "backend" folder, and its subfolder "_scss" (because I believed this issue was something CSS-related). And finally, I stopped at a config file . "Ahhh, that's how people stored CSS variables for easier changing in future" -- I thought. I scrolled through the file and I saw a variable called "navbar-color".