4
I did an example of CSS code to learn a little bit more about the use of classes. However, I realized a mistake and I can’t quite understand why.
1° example
.fonte-style-h1 {
	vertical-align: middle;
	font-size: 30%;
	color: yellow;
	text-shadow: -1px 0 black, 0 1px black, 1px 0 black, 0 -1px black;
}<!DOCTYPE html>
<html>
<head>
	<title>CSS</title>	
</head>
<body>	
	<h1 class=".fonte-style-h1">Oie CSS!</h1>	
</body>
</html>Note in this example I created the class .fonte-style-h1 to define a style for tag content h1 and see that there was no effect.
2° example
h1 {
	vertical-align: middle;
	font-size: 250%;
	color: seagreen;
	text-shadow: -1px 0 black, 0 1px black, 1px 0 black, 0 -1px black;	
}<!DOCTYPE html>
<html>
<head>
	<title>CSS</title>	
</head>
<body>	
	<h1>Oie CSS!</h1>	
</body>
</html>In this second example see that I applied style to the tag h1 in a general way and it worked. It is at this point that my doubt arises.
Question
Why class .fonte-style-h1 does not apply style to tag h1 and when I use h1 instead of the class it works?
A hint is that the same one applies to the ID, where in the . CSS would be
#nome-do-id {estilos}and in HTML you would have<elemento id="nome-do-id">thenid="#nome-do-id"would also be wrong.– hugocsl