How to learn advanced CSS ? And what does this code mean?

[marina_khamis]

I created an account on “CSS Battles”, And I was curious about the answer of the highest score in the first battle," Battle #1 - Pilot Battle #1 - Simply Square" The code was like that :

<img style=box-shadow:0+0+0+2in#b5e0ba,0+0+0+5in#5d3a3a>

Which creates a square that looks like this :

So what does the code mean? and how to learn advanced things like that?
And what search keywords should I use to look these things out in google ?

[lasjorg]

It is the same as:

img {
  box-shadow: 0 0 0 2in #b5e0ba, 0 0 0 5in #5d3a3a;
}

First box-shadow:

0 offset-x
0 offset-y
0 blur-radius
2in spread-radius
color #b5e0ba

Second box-shadow:

0 offset-x
0 offset-y
0 blur-radius
5in spread-radius
color #5d3a3a

https://developer.mozilla.org/en-US/docs/Web/CSS/box-shadow

The in unit is inches.

https://developer.mozilla.org/en-US/docs/Web/CSS/length

The use of + is to avoid having to use a string.

<img style="box-shadow:0 0 0 2in #b5e0ba,0 0 0 5in #5d3a3a">

You can search for css golf code to read more.

Example article

A CSS Golfing Exercise | CSS-Tricks

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Just to be clear, golf code can be interesting but it isn’t very useful in the real world.

[marina_khamis]

@lasjorg That was very detailed and useful! Thank you so much