2-1 佈局頁面

一、嚮應式斷點：Bootstrap4 為行動優先的架構，所以預設的斷點為 (xs)

// Extra small devices (portrait phones, less than 576px)
// No media query since this is the default in Bootstrap

// Small devices (landscape phones, 576px and up)
@media (min-width: 576px) { ... }

// Medium devices (tablets, 768px and up)
@media (min-width: 768px) { ... }

// Large devices (desktops, 992px and up)
@media (min-width: 992px) { ... }

// Extra large devices (large desktops, 1200px and up)
@media (min-width: 1200px) { ... }

二、container(固定寬度)

1. 最大寬度(xs-576)：540px
2. 最大寬度(sm-768)：720px
3. 最大寬度(md-992)：960px
4. 最大寬度(lg-1200)：1140px

三、container-fluid(滿版寬度)