Negative

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.

Default Units on CSS and attribute

This example demonstrates that:

• the unit is mandatory in CSS (If the length does not have any unit, the property is discarded and takes the default values)
• the unit default to pixel on attribute

Example code:

• width and height with a length without unit

.box {
   width:10;
   height:10;
}

• the html with :
  • a div where the css rule will apply
  • an img with width and height attribute without a length of 50 without unit

<div class="box">
   <img src="/_media/web/rss_icon.jpg" height="50" width="50" />
</div>

</code>

• The computed width and height for the div box is shown below via this javascript

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);

• The computed width and height for the image is shown below via this javascript

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);

• Result: we can see that:
  • the css width and height are not 10 but the default values: ie
    • the full available width
    • a zero height.
  • the img sizing has taken the default pixel unit