There is a line of space before every list i create, number or bullet…
How could i cancel this space?
I have absolutely no experience in css file, so i looked online copied a css file into the obsidian vault but did not worked 
If you mean the space above a list in Reading mode, this CSS gets rid of it in general:
:has(+ .el-ol) > p,
:has(+ .el-ul) > p,
:has(+ .el-ol) > .callout,
:has(+ .el-ul) > .callout {
margin-block-end: 0;
}
.el-ol > ol,
.el-ul > .has-list-bullet {
margin-block-start: 0;
}
There could be circumstances where that doesn’t work; I only tested in the sandbox with paragraphs and callouts before it. Hope it helps. But if you meant something else, maybe show a screenshot and describe it more.
Default in sandbox:
With snippet:
