how to make css in text box code example

Example 1: how do i make a boxin html

<div style="width:500px;height:100px;border:1px solid #000;">This is a rectangle!</div>

Example 2: style input field

#userInfoForm {
    width: 80%;
    padding: 5px 5px;
    margin: 0 auto;
    background: #FF6700;
    border-radius: 25px; 
}

#userInfoForm input {
    width: 100%;
    padding: 12px 20px;
    margin: 8px 0;
    box-sizing: border-box;
    border-radius: 25px;
}