If IDs in HTML should be unique, why sometimes I s

问题:

Since an ID should be unique in HTML, why sometimes i see in Css selectors formatted like (div#nav-blue), since it's obvious that there will be no other element having this ID exccept for that div, so aint writting #nav-blue makes more sense?

回答1:

It does no change or a little.

You can do this for some reason : more visibility when you maintain your code. Easier to find, and remember for each kind of element is the style.

The second reason is the priority of selector.

There is some different order of priority :

!important > #id > .class > element

you can consider that

 element = 1
 .class = 10
 #id = 100
 !important= 1000

And then div#id = 101 > #id = 100

div#myid{
  color:red;
}

#myid{
  color:blue;
}

.myclass{
  color:yellow;
}

div{
  color:green;
}

<div class="myclass" id="myid">
Some text
</div>