So… actually, this unitless value do correspond to a percentage (according to MDN):
font-size: 10px;
line-height: 1.2; /* 12px /
line-height: 1.2em; / 12px /
line-height: 120%; / 12px */
It’s all the same.
So, in the end, you were right, guy.

I can only find the value “none” mentioned in a spec that’s almost 15 years old:
https://www.w3.org/TR/2002/WD-css3-linebox-20020515/#line-height

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well u can use span tag for container bt as per my knowledege we can not set width and height of inline container bcz inline Element only take space that is bounded by its tags. that why there is div (block level) element for container.

`CSS offers one other measurement method specific to line height, which is simply
a number. You write it like this:

line-height: 1.5;

There’s no unit (like em or px) after this value. The browser multiplies this number by the font size to determine the line height. So if the text is 1em and the line-height value is 1.5, then the calculated line height is 1.5em. In most cases, the effect is no different from specifying a value of 1.5em or 150%. But sometimes this multiplication factor comes in handy, especially since nested tags inherit the line-height value of their parents.

For example, say you set the line-height property of the tag to 150%. All tags inside the page would inherit that value. However, it’s not the percentage that’s inherited; it’s the calculated line height. So, say the font size for the page is set to 10 pixels; 150 percent of 10 is 15 pixels. Every tag would inherit a line height of 15 pixels, not 150 percent. So if you happened to have a paragraph with large, 36 pixel text, then its line height—15 pixels—would be much smaller than the text, making the lines squish together in a hard-to-read mess.

In this example, instead of using a line-height of 150% applied to the tag, you could have all tags share the same basic proportional line height by setting the line-height to 1.5. Every tag, instead of inheriting a precise pixel value for line height from the body style, simply multiplies its font size by 1.5. So in the above example of a paragraph with 36-pixel text, the line height would be 1.5 x 36 or 54 pixels.

I did find it in the W3C working draft, mentioned as a special property.

Neither MDN nor W3C mention none as a valid value for line-height

Here is the answer https://developer.mozilla.org/en-US/docs/Web/CSS/line-height

1.5 is not the same as 150%.

What is line height? Percent, pixel value?

What is the formula for taking a line of a given height and finding it’s new height based on a unitless line height?