[SOLVED] Can I select an element based on a data value greater than comparison?

Can I select an element based on a data value greater than comparison?

<div data-age="30">30</div>

Is there a way to have (PURE CSS) div in red when age<18 and in blue where age>18

Solution

Now with conditional statement support in the background property, we can do it. This currently has limited support; use Chrome (version 138+) to test:

@property --a {
  syntax: "<number>";
  inherits: false;
  initial-value: 0; 
}

.box {
  --a: sign(attr(data-age type(<number>)) - 17);
  background: if(style(--a: 1): blue; else: red);

  font-size: 30px;
  padding: 5px;
  display: inline-block;
  font-family: monospace;
  color: #fff;
}

.box::before {
  content: attr(data-age);
  display: inline-block;
}

<div data-age="30" class="box"></div>
<div data-age="18" class="box"></div>
<div data-age="9" class="box"></div>
<div data-age="17" class="box"></div>
<div data-age="0" class="box"></div>

Old answer

Here is an idea based on this previous answer where you can consider CSS variables:

.box {
  font-size:30px;
  padding:5px;
  display:inline-block;
  font-family:monospace;
  overflow:hidden;
  color:#fff;
  background:
     linear-gradient(red,red) 0 0/100% calc((18 - var(--a))*1px),
     blue;
}
.box:before {
  content:attr(style);
  text-indent:-4ch;
  display:inline-block;
}

<div style="--a:30" class="box"></div>
<div style="--a:18" class="box"></div>
<div style="--a:9 " class="box"></div>
<div style="--a:17" class="box"></div>
<div style="--a:0 " class="box"></div>

You can also do it for text coloration:

.box {
  font-size:30px;
  padding:5px;
  display:inline-block;
  font-family:monospace;
  overflow:hidden;
  border:5px solid transparent;
  background:
     linear-gradient(#fff,#fff) padding-box,
     linear-gradient(red,red) 0 0/100% calc((18 - var(--a))*1px),
     blue;
}
.box:before {
  content:attr(style);
  text-indent:-4ch;
  display:inline-block;
  color:transparent;
  background:
     linear-gradient(red,red) 0 0/100% calc((18 - var(--a))*1px),
     blue;
  -webkit-background-clip: text;
  background-clip: text;
  -webkit-text-fill-color: transparent;
}

<div style="--a:30" class="box"></div>
<div style="--a:18" class="box"></div>
<div style="--a:9 " class="box"></div>
<div style="--a:17" class="box"></div>
<div style="--a:0 " class="box"></div>