I prefer the vanilla CSS. I'll share and tell my bad experience with Bootstrap framework. I used to make part of a team which used to contain only two persons — one CEO and one iOS app developer. Before I entered in their team or they knew me, the iOS developer used to take care about their new site, but he did not understand the web development and made numerous mistakes in their site. I saw their new social project, was interested and sent feedback to them for improving their new site. But I did not imagine he has used Bootstrap. Then I joined their chat group and sent feedback to them. When I told I have been newly graduated in computer science and worked with IT areas, they have been interested, contacted me and invited me to make part of their team. The iOS developer delivered me their new site in my hands. I found numerous mistakes and discovered he used Bootstrap. I corrected and fixed hundred of mistakes, reorganised the CSS, optimised the site, replacing some unnecessary things for pure CSS. But I discovered that he also created hard-coded third-party codes, what made the site unfriendly to the responsive design. He also forgot the importance of UI/UX design principles and of accessibility (blind people, dark mode for people with photophobia like me and deaf-born people like me). Due to some hard-coding and the unfriendliness of the site to the responsive design, unfortunately Bootstrap and the hardcoding forced me to use terms of multiple fixed width layouts. I knew it is very bad idea, then I was screwed up. Then I redesigned the site for the mobile phones with less than 240px and less than 412px, and discovered that that one media query was not loaded. I and my best friend from Canada investigated and spent hours, trying to figure the cause. We thought it were other fixed media queries, but did not imagine it was Bootstrap. That forced me to create the separated CSS files and add links to HTML file's head, and they were loaded. Until the second query was not loaded, I did not understand. I and the Canadian investigated again, and I discovered that it was Bootstrap , because Bootstrap used max-width: 991px , which includes all the phones and tablets, bypassed these media queries and prevented them from loading. After all that, I have had a very long talk with my best friend from Canada. He analysed both the original and new (with frameworks) sites, and said he was going to facilitate the original site, but hours later, he told me he gave up, because he said Bootstrap has many breakpoints, what mean much complexity. He said big or small changes, even if with Bootstrap, also mean complexity, and high complexity results in a big number of bugs. Bootstrap hides complexity and the people are unaware of that. He understood perfectly my pain, my sufferance and my insanity when I deal with Bootstrap. Finally, I do not want to deal with Bootstrap problems. I can not maintain the mixed CSS. CSS using mixed Bootstrap and third-party codes is unmaintainable and unsustainable .