css - Problems using class selectors

Question

1. I just started to learn HTML and CSS by myself. I wanted to define two fonts in one block. I used the class selector, but after defining it, I didn’t see any change in the font on the page (it was still the default size and color). ), is it the selector or the code that is wrong? இ௰இ

2This is the html code

<p id="container">

       <p id="header">
          <p id="Love Live Sunshine">
              <p>
                                <h1>Love Live Sunshine</h1>
                                <hr width="960&">
                                <p>这是一个标题！！！</p>
              </p>
           </p> 
        </p>

This is the CSS

Please forgive me

Answer 1

Use ID less, and don’t use it so long because ID is unique, so long is meaningless. Then don’t add dots in front of h1 and p, dots are for class selection

Answer 2

Please use - instead of spaces
There is also this called ID selector and class selector is class

Answer 3

Do not include spaces in the id

Answer 4

Just change . to a space = =
. The beginning is the class selector. You need to write CSS for the label here. There is no need for any prefix in front of the label

Answer 5

In addition to clear grammar specifications and selector properties, remember to introduce style files