断点

核心理念

🌐 Core concepts

• 断点是响应式设计的基础模块。 使用它们来控制你的布局在特定视口或设备尺寸下的适应时机。
• 使用媒体查询按断点构建你的 CSS。 媒体查询是 CSS 的一个功能，它允许你根据一组浏览器和操作系统参数有条件地应用样式。我们最常在媒体查询中使用 min-width。
• 移动优先，响应式设计是目标。 Bootstrap 的 CSS 旨在应用最少的样式以使布局在最小的屏幕断点下正常工作，然后逐层增加样式以调整大屏设备的设计。这可以优化你的 CSS，提高渲染速度，并为访客提供良好的体验。

可用断点

🌐 Available breakpoints

Bootstrap 包括六个默认的断点，有时称为 网格层，用于构建响应式布局。如果你使用我们的源 Sass 文件，这些断点可以自定义。

🌐 Bootstrap includes six default breakpoints, sometimes referred to as grid tiers, for building responsively. These breakpoints can be customized if you’re using our source Sass files.

每个断点的选择是为了能够轻松容纳宽度为12倍数的容器。断点还代表了一部分常见设备尺寸和视口尺寸——它们并不针对每种使用情况或设备。相反，这些范围为几乎所有设备提供了坚实而一致的基础。

🌐 Each breakpoint was chosen to comfortably hold containers whose widths are multiples of 12. Breakpoints are also representative of a subset of common device sizes and viewport dimensions—they don’t specifically target every use case or device. Instead, the ranges provide a strong and consistent foundation to build on for nearly any device.

这些断点可以通过 Sass 自定义——你会在我们的 _variables.scss 样式表的一个 Sass 映射中找到它们。

🌐 These breakpoints are customizable via Sass—you’ll find them in a Sass map in our _variables.scss stylesheet.

$grid-breakpoints: (
  xs: 0,
  sm: 576px,
  md: 768px,
  lg: 992px,
  xl: 1200px,
  xxl: 1400px
);

有关如何修改我们的 Sass 映射和变量的更多信息和示例，请参阅网格文档的 CSS 部分。

🌐 For more information and examples on how to modify our Sass maps and variables, please refer to the CSS section of the Grid documentation.

媒体查询

🌐 Media queries

由于 Bootstrap 的开发是以移动设备优先的，我们使用了一些 媒体查询 来为我们的布局和界面创建合理的断点。这些断点主要基于最小视口宽度，并允许我们随着视口的变化缩放元素。

🌐 Since Bootstrap is developed to be mobile first, we use a handful of media queries to create sensible breakpoints for our layouts and interfaces. These breakpoints are mostly based on minimum viewport widths and allow us to scale up elements as the viewport changes.

最小宽度

🌐 Min-width

Bootstrap 主要在我们的布局、网格系统和组件的源 Sass 文件中使用以下媒体查询范围（或断点）。

🌐 Bootstrap primarily uses the following media query ranges—or breakpoints—in our source Sass files for our layout, grid system, and components.

// Source mixins

// No media query necessary for xs breakpoint as it’s effectively `@media (min-width: 0) { ... }`
@include media-breakpoint-up(sm) { ... }
@include media-breakpoint-up(md) { ... }
@include media-breakpoint-up(lg) { ... }
@include media-breakpoint-up(xl) { ... }
@include media-breakpoint-up(xxl) { ... }

// Usage

// Example: Hide starting at `min-width: 0`, and then show at the `sm` breakpoint
.custom-class {
  display: none;
}
@include media-breakpoint-up(sm) {
  .custom-class {
    display: block;
  }
}

这些 Sass 混入在我们编译的 CSS 中会使用我们在 Sass 变量中声明的值进行转换。例如：

🌐 These Sass mixins translate in our compiled CSS using the values declared in our Sass variables. For example:

// X-Small devices (portrait phones, less than 576px)
// No media query for `xs` 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) { ... }

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

// XX-Large devices (larger desktops, 1400px and up)
@media (min-width: 1400px) { ... }

最大宽度

🌐 Max-width

我们偶尔会使用指向相反方向的媒体查询（给定屏幕尺寸_或更小_）：

🌐 We occasionally use media queries that go in the other direction (the given screen size or smaller):

// No media query necessary for xs breakpoint as it’s effectively `@media (max-width: 0) { ... }`
@include media-breakpoint-down(sm) { ... }
@include media-breakpoint-down(md) { ... }
@include media-breakpoint-down(lg) { ... }
@include media-breakpoint-down(xl) { ... }
@include media-breakpoint-down(xxl) { ... }

// Example: Style from medium breakpoint and down
@include media-breakpoint-down(md) {
  .custom-class {
    display: block;
  }
}

这些 mixin 使用已声明的断点，从中减去 .02px，并将其用作我们的 max-width 值。例如：

🌐 These mixins take those declared breakpoints, subtract .02px from them, and use them as our max-width values. For example:

// `xs` returns only a ruleset and no media query
// ... { ... }

// `sm` applies to x-small devices (portrait phones, less than 576px)
@media (max-width: 575.98px) { ... }

// `md` applies to small devices (landscape phones, less than 768px)
@media (max-width: 767.98px) { ... }

// `lg` applies to medium devices (tablets, less than 992px)
@media (max-width: 991.98px) { ... }

// `xl` applies to large devices (desktops, less than 1200px)
@media (max-width: 1199.98px) { ... }

// `xxl` applies to x-large devices (large desktops, less than 1400px)
@media (max-width: 1399.98px) { ... }

单断点

🌐 Single breakpoint

还有媒体查询和混合，用于使用最小和最大断点宽度来定位屏幕尺寸的单段。

🌐 There are also media queries and mixins for targeting a single segment of screen sizes using the minimum and maximum breakpoint widths.

@include media-breakpoint-only(xs) { ... }
@include media-breakpoint-only(sm) { ... }
@include media-breakpoint-only(md) { ... }
@include media-breakpoint-only(lg) { ... }
@include media-breakpoint-only(xl) { ... }
@include media-breakpoint-only(xxl) { ... }

例如，@include media-breakpoint-only(md) { ... } 将导致：

🌐 For example the @include media-breakpoint-only(md) { ... } will result in :

@media (min-width: 768px) and (max-width: 991.98px) { ... }

断点之间

🌐 Between breakpoints

同样，媒体查询可能跨越多个断点宽度：

🌐 Similarly, media queries may span multiple breakpoint widths:

@include media-breakpoint-between(md, xl) { ... }

结果是：

🌐 Which results in:

// Example
// Apply styles starting from medium devices and up to extra large devices
@media (min-width: 768px) and (max-width: 1199.98px) { ... }