when i change a site (index.html), all the other (sub)sites change also with the same settings. how can i made changes in, for example index.html so that other (sub)sites do not change?
i see that the file extension is .css when i make an new site. then i save the site to index.html and the other sites changes also when i made changes in index.html (i mean the settings)
I'm not sure exactly what you are asking, but it sounds like you are making changes to a cascading stylesheet (a .css file) that is shared by several pages on your site, but ony want to make the change to the style on the home page.
You can do this by adding inline css to the home page elements you want to be styled differently from the rest of your site.
An example of an inline css definition would be something like this...
<div id="content" style="background-color:blue;">
In the above example, the div would be styled using whatever you have written for the #content id in your css. It would also then overwrite any background-color declared in the external .css file with the style attribute to make the background blue.
I'm not sure I understand this question but I'll attempt to answer you anyway.
When you change styles in your CSS code, those styles cascade down to other site pages. That's how site wide style sheets are supposed to work.
If you want to create a unique style, define a CSS .class for it.
<h1 class="special_page_1_style">Special style applied here</h1>