【5】Understand Bootstrap's preset grid system_html/css_WEB-ITnose

Before we start, let’s talk about a class, because it will be used later

<div class="container">  ...</div>

You can wrap the content on the page with .container. Center aligned. The width of the container is set within different media query thresholds to match the grid system.

Note: Due to the padding and fixed width settings, .container cannot be nested.

Some people here may not know what "different media query threshold ranges" are? What I want to say here is that a set of ranges is defined (this range has several intervals). If the browser width value (i.e., the visual area) you are currently using is within a certain interval of this set of ranges, then use this The solution for browsing web pages in intervals. (I don’t know if I can make people understand by saying this, sweat￣□￣｜｜)

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【1】Let’s introduce the grid system (excerpt from the official website)

Bootstrap has a built-in responsive, mobile-first fluid grid system. As the screen device or viewport size increases, the system will automatically be divided into up to 12 columns.

1. It contains easy-to-use predefined classes (this is what we are talking about, I don’t know if it is an official Chinese typo, why is there an extra e after class);

2 , and there are powerful mixins used to generate more semantic layouts (this is not what we are talking about, it is equivalent to customizing the grid layout you want, the default preset classe is enough for us, if you want to go further , you can study it yourself).

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【2】The grid system is used to create a page layout through a series of combinations of rows and columns, and your content can be placed into the created layout.

The following is an introduction to the working principle of the following Bootstrap grid system:

1. "Row" must be included in the .container in order to give it the appropriate alignment and Padding.
2. Use "row" to create a group of "columns" in the horizontal direction.
3. Your content should be placed within "column", and only "column" can be used as a direct child element of row.
4. Through some predefined Grid classes (.row and .col-xs-4) can be used to quickly create grid layouts. The mixins defined in the Bootstrap source code can also be used to create semantic layouts.
5. Create "by setting padding." "Gutter" between "columns". Then offset the effect of padding by setting negative margins for the first and last.
6. The columns in the grid system are specified by specifying 1 to 12 value to represent the range it spans. For example, three equal-width columns can be created using three .col-xs-4

full-screen layout methods:

for those that need to occupy the entire. For browser viewport pages, the content area needs to be wrapped in a container element and given padding: 0 15px; in order to offset the margin: 0 -15px; set for .row (if not If so, your page will be 15px beyond the viewport, and a horizontal scroll bar will appear at the bottom of the page)

ps. To be honest, I didn’t understand a few sentences in the pile above, but I generally understand them. Those who don’t understand can only understand it through the following exercises. Of course, the use of this grid reminds me of using Excel tables. ================================================== ==============================

I have excerpted so many official websites, and we will discuss them again at the beginning. When we talked about "different media query threshold ranges", that is, the grid option, let's take a look at it!

【3】The grid option is how Bootstrap's grid system works on multiple screens. It works on the equipment. Let’s take a look at the table given by the Chinese official website

From the table we can see that there are 4 intervals corresponding to our own equipment. We assume that The view area is x.

The grid class works on devices with a screen width greater than or equal to the threshold, and will override the class set for small screen devices. Therefore, it is applied to any element. Any .col-md- (begins with) class will work not only on medium-sized screens, but also on large-screen devices (if no .col-lg- (begins with) class is set)

lg	large（大）	x≥1200px	桌面
md	middle（中）	992px≤x＜1200px	桌面
sm	small（小）	768px≤x＜992px	平板
xs	extra small（极小，网上找的，不知道有没有更合适的）	x＜768px	手机