demo : https://www.lenlop123.com/2020/09/10-style-css.html

<!--more--><br />


<style>
    #div_1 {
        color: blueviolet;
    }

    .div_2{
        color: brown;        
    }

    p{
        color: deeppink;
    }

    a.a_a1:hover {
        color: red;
        text-decoration: none;
    }
</style>

<div id="div_1">
    Css theo id : #div_1 {}
</div>

<div class="div_2">
    Css theo classname : .div_2{}
</div>

<p> Css theo tag :  p{} </p>

<div>
    <a class="a_a1" href="http://www.sololearn.com" target="_blank">
        Css theo tag và classname : a.a_a1:hover {}
    </a>
</div>

<div style="background-color: aqua;">Css theo style : style="" </div>