Front-end basics??CSS DIV layout_html/css_WEB-ITnose

Just open a webpage and press F12, and you will find a bunch of dense "DIVs". Yes, most webpages now use CSS DIV layout.

The previous article talked about the box model. Here we will use the box model as the basis to briefly understand a commonly used web page layout method: CSS DIV layout.

CSS DIV layout is to use the

tag to divide the page into several blocks as a whole, then perform CSS positioning on each

block, and finally add corresponding content to each block.

Just like building a steel structure building, first build the frame of the entire web page, and then refine the parts separately. Here

is like a steel bar, responsible for building the frame, and CSS is Equivalent to the rules of construction, the steel bars are welded according to certain rules (i.e. business requirements).

                                                                                  Divided into two steps:

1. To choose materials, you must have some understanding of the steel bars to be used, that is, understand DIV

I had a friend before Asked me: "What is the box model, is it a DIV?" I rejected him. In the author's opinion, many elements in the web page can be regarded as a "box", such as p, h1, form, div, span, table, tr, td, etc., they all have margin, border, padding attributes.

It’s just that when we build the overall web page layout, we generally use DIV to act as the “rebar” in the above example.

The box model is the basis and key of DIV CSS. To put it simply, the core of the box model lies in the margin, border, and padding attributes of those "boxes". This is the basic skill if you want to lay out a reasonable and beautiful web page.

2. Cutting and welding materials

The material is cut (designing DIVs of different sizes) and welded (using CSS to position the corresponding DIVs).                                                                                                                                                                                                                                                                                                        .

The focus here is welding. When welding, you need to select DIV blocks of different sizes and place them reasonably, which is called DIV positioning, including the positioning of DIV Settings of position, float, and z-index properties.

Position attribute: The four attribute values ​​are static, absolute, relative, and fixed. The following table is the W3C description of these attribute values:

Value	Description
static	Default value. Without positioning, the element appears in normal flow (ignoring top, bottom, left, right or z-index declarations).
inherit	Specifies that the value of the position attribute should be inherited from the parent element.                                                                                                                                                                                                                                                . The position of the element is specified through the "left", "top", "right" and "bottom" attributes.
relative	Generates a relatively positioned element, positioned relative to its normal position. So "left:20" adds 20 pixels to the element's LEFT position.
fixed	Generates absolutely positioned elements, positioned relative to the browser window. The position of the element is specified through the "left", "top", "right" and "bottom" attributes.

Generally speaking, when the value of the position attribute of an element is absolute or fixed, it is no longer constrained by the parent element and is positioned only based on the values ​​of left, top, right and bottom of the page.

The float attribute has four attribute values: left, right, none, inherit: td>Value

Description none Default value. The element is not floated and appears where it appears in the text. inherit Specifies that the value of the float attribute should be inherited from the parent element.

left The element floats to the left. right The element floats to the right.

值	描述
none	默认值。元素不浮动，并会显示在其在文本中出现的位置。
inherit	规定应该从父元素继承 float 属性的值。
left	元素向左浮动。
right	元素向右浮动。

No more details. Students who are unclear can make a few small examples to practice by themselves, or go to W3School to practice, here There are rich web tutorials and some small examples that can be practiced online.

Float is the difficulty and key point here. I hope readers can master it proficiently.

                                                                                                                                          ’ ’ s ’ s ’ s ’s ’ s ’ s -                                                                                      Level", the larger the value, the higher the priority displayed. Two simple pictures are enough to illustrate:

                                                                                                                                                                                                                                                                           The z-index values ​​of the three divs in the picture are: A>B>C.

These are just the most basic knowledge of the CSS DIV layout. If you want to truly eat it, you also need to continue to practice and experience some tips for layout. For example, using negative values ​​for margin is a very practical trick. If you want the container to be displayed with a fixed width in the center (assuming the container width is 700px), you can use the relative positioning method for the container, and the left value is 50% of the page, and then set The margin-left is half of its own width. In this way, the display effect is fixed width and centered no matter what browser resolution is used, as shown below:

                                           When not enough is displayed, how to keep the bottom footer (copyright registration part) always at the bottom can also be achieved by setting a negative value for margin.

Accumulate more and look forward to growing together with you.