Lengths refer to horizontal or vertical measurements.
The format of a length value is a number (with or without a decimal point) immediately followed by a unit identifier
number unit
where:
In sizing attribute such as width and height, there is a default unit and this is the pixel. This is also the default Svg unit
Some properties allow negative length values, but this may complicate the formatting model and there may be implementation-specific limits. If a negative length value cannot be supported, it should be converted to the nearest value that can be supported.
If a negative length value is set on a property that does not allow negative length values, the declaration is ignored.
This example demonstrates that:
Example code:
.box {
width:10;
height:10;
}
<div class="box">
<img src="/_media/web/rss_icon.jpg" height="50" width="50" />
</div>
</code>
let box = document.querySelector('.box');
let styles = window.getComputedStyle(box);
let width = styles.getPropertyValue("width");
let height = styles.getPropertyValue("height");
console.log("The computed css width is "+width);
console.log("The computed css height is "+height);
let img = document.querySelector('img');
let imgStyles = window.getComputedStyle(img);
let widthImg = imgStyles.getPropertyValue("width");
let heightImg = imgStyles.getPropertyValue("height");
console.log("The computed img width is "+widthImg);
console.log("The computed img height is "+heightImg);