how to change html class background code example

Example 1: html create class

<h1 class="write a name">H1 content</h1>

Example 2: syntax for manipulating a class in css

//element
element {
}
//class
.class {
}
//ID
#id {
}
//element and class
element .class {
}
//element with class and decendent
element.class decendent {
}