No stupid questions here.
The trick to using CSS is
selecting the thing you want styled. Everything before the curly brace is a selector. Since we're styling HTML, we've got lots of little tags, all exactly alike, nested within each other. Picking the exact one you want to style can get a little tricky.
Luckily, we've got three different names for any tag: the tag type (like div, span, or p), the tag's class (specified with class="the_class"), and the tag's ID (specified with id="the_id"). Since you could give something the same class a a tag (like, <li class="div">), we need a way to specify which one we're talking about when we write our CSS rules.
To specify a tag type, just write it (as in div). To specify a tag class, use a period (as in .the_class). To specify a tag ID, use the octothorpe (as in #the_id). (And aren't you impressed with my vocabulary?

)
These three things alone give us a lot of power to indicate a particular tag or group of tags. For instance, if you wanted to make all the comment text white, just assign it the class "comment_text", then write a CSS rule like this:
There are other attributes you can change, too. Google up a CSS tutorial for more detail.
Despite this power, we need more. CSS also lets us pick a tag inside another tag with the space character. So, given HTML like this:
Code: Select all
<ul class="myList">
<li class="myBullet">A <b>bullet</b> item</li>
</ul>
We can specify only "myBullet"s inside "myList"s with a space character:
You can nest as deeply as you like. The item can be anywhere inside the container. Since the <b> tag above is inside the <li> with class myList, this will work too:
So the "input" you were looking at was specifying an <input> tag contained within an item whose ID was "serendipity_whatever". There must have been something with the ID "serendipity_whatever", which you wanted to style, but no <input> inside it. When you removed the input, the whatever got styled.
Some browsers support other stuff, but almost all browsers support at least this much. There is more syntax you can look at, and other rules, and WAY more attributes. Once again, Google is your friend.
Hope that helps!