http://stackoverflow.com/questions//container-fluid-vs-container
https://www.jquery-az.com/bootstrap-container-and-container-fluid-what-is-the-difference/
.container 类是固定宽度的容器。这并不意味着它没有响应。它反应灵敏；但是，它是根据屏幕尺寸固定的。屏幕尺寸包括：
xs for extra small devices (used for less than 768 e.g smart phones, mobile etc.) sm for small screens (From 768 pixels and up e.g. tablets) md for the medium screen (>= 992 pixels. Desktops/Laptops) lg for large screens (>= 1200. Pixels e.g. large desktops)容器流体类将占据视口的整个宽度。如果您使用 container-fluid 并调整浏览器的大小，您可能会注意到其中的内容会随着每个像素进行调整以占据完整的可用宽度。