Why does the order of media queries matter in CSS?
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.
Here's an example:
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;}
}
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;}
}
If my understanding of media queries are correct, the order shouldn't matter, but it seems it does. What could be the reason?
Answer
That's by design of CSS — Cascading Style Sheet.
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).
So, given this CSS
@media (max-width: 600px) {
body {
background: red;
}
}
@media (max-width: 400px) {
body {
background: blue;
}
}
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;
}
}
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.
Finally, with
@media (max-width: 400px) {
body {
background: blue !important;
}
}
@media (max-width: 600px) {
body {
background: red;
}
}
or
@media (max-width: 400px) {
html > body {
background: blue;
}
}
@media (max-width: 600px) {
body {
background: red;
}
}
the background will be blue (with a 350 pixels wide window).