为什么CSS中的媒体查询顺序很重要？ [英] Why does the order of media queries matter in CSS?
问题描述
最近，我一直在设计更具响应性的网站，并且经常使用CSS媒体查询。我注意到的一种模式是媒体查询的定义顺序实际上很重要。我没有在每个浏览器中测试它，只是在Chrome上。这个行为有解释吗？有时，当您的网站无法正常工作时，您会感到沮丧，您不确定是查询还是查询的书写顺序。
Of late, I've been designing sites that are more responsive and I've been using CSS media queries frequently. One pattern I noticed is that the order in which the media queries are defined actually matters. I didn't test it in every single browser, but just on Chrome. Is there an explanation for this behaviour? Sometimes it gets frustrating when your site doesn't work as it should and you are unsure if it's the query or the order in which the query is written.
这里是一个示例：
HTML
<body>
<div class="one"><h1>Welcome to my website</h1></div>
<div class="two"><a href="#">Contact us</a></div>
</body>
CSS：
body{
font-size:1em; /* 16px */
}
.two{margin-top:2em;}
/* Media Queries */
@media (max-width: 480px) {
.body{font-size: 0.938em;}
}
/* iphone */
@media only screen and (-webkit-min-device-pixel-ratio: 2) {
body {font-size: 0.938em;}
}
/*if greater than 1280x800*/
@media (min-width: 1200px) {
.two{margin-top:8em;}
}
/*1024x600*/
@media (max-height: 600px) {
.two{margin-top:4em;}
}
/*1920x1024*/
@media (min-height: 1020px) {
.two{margin-top:9em;}
}
/*1366x768*/
@media (min-height: 750px) and (max-height: 770px) {
.two{margin-top:7em;}
}
然而，如果我在最后写入1024x600的查询，浏览器将忽略它，并应用CSS开始时指定的margin值（margin-top：2em）。
However, If I wrote the query for 1024x600 in the last, the browser would ignore it and apply the margin value specified in the starting of the CSS (margin-top:2em).
/* Media Queries - Re-arranged version */
@media (max-width: 480px) {
.body{font-size: 0.938em;}
}
/* iphone */
@media only screen and (-webkit-min-device-pixel-ratio: 2) {
body {font-size: 0.938em;}
}
/*if greater than 1280x800*/
@media (min-width: 1200px) {
.two{margin-top:8em;}
}
/*1920x1024*/
@media (min-height: 1020px) {
.two{margin-top:9em;}
}
/*1366x768*/
@media (min-height: 750px) and (max-height: 770px) {
.two{margin-top:7em;}
}
/*1024x600*/
@media (max-height: 600px) {
.two{margin-top:4em;}
}
如果我对媒体查询的理解正确，顺序不重要，它似乎它。可能的原因是什么？
If my understanding of media queries are correct, the order shouldn't matter, but it seems it does. What could be the reason?
推荐答案
这是由CSS设计的层叠样式表。
That's by design of CSS — Cascading Style Sheet.
这意味着，如果你应用两个碰到相同元素的规则，它将选择最后一个被声明的规则，除非第一个规则具有！important marker或更具体（例如 html> body vs body ，后者不太具体）
It means that, if you apply two rules that collide to the same elements, it will choose the last one that was declared, unless the first one has the !important marker or is more specific (e.g. html > body vs just body, the latter is less specific).
因此，给定此CSS
@media (max-width: 600px) {
body {
background: red;
}
}
@media (max-width: 400px) {
body {
background: blue;
}
}
如果浏览器窗口宽350像素，将为蓝色，而使用此CSS
if the browser window is 350 pixels wide, the background will be blue, while with this CSS
@media (max-width: 400px) {
body {
background: blue;
}
}
@media (max-width: 600px) {
body {
background: red;
}
}
和相同的窗口宽度，背景将是红色。
and the same window width, the background will be red. Both rules are indeed matched, but the second one it's the one that is applied because is the last rule.
最后，使用
@media (max-width: 400px) {
body {
background: blue !important;
}
}
@media (max-width: 600px) {
body {
background: red;
}
}
或
@media (max-width: 400px) {
html > body {
background: blue;
}
}
@media (max-width: 600px) {
body {
background: red;
}
}
背景将是蓝色的窗口）。
the background will be blue (with a 350 pixels wide window).
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