javascript - How to make the outer div adaptively adjust its width according to the width of the inner div

Question

It is best to use pure html css, pseudo code example:

<p id="1">
    <p id="2"></p>
    <p id="3">
        <ul></ul>
    </p>
</p>

Let the width of the outer layer p1 change with the width of the inner layer p

Answer 1

Thanks for the invitation.

<style>
#a {
    border: 1px solid red;
    display: inline-block;
}

#b {
    border: 1px solid green;
    margin: 2px 2px 2px 2px;
    height: 50px;
    width: 500px;
}
</style>
<p id="a">
    <p id="b"></p>
    <p id="c">
        <ul></ul>
    </p>
</p>

Answer 2

<style>
 #1 {
  display: inline-block;
 }
</style>

Answer 3

#1{
   float:left;
}