CSS padding as hover effect-CodePudding

I have successfully set a hover and the effect works in principle. Unfortunately, however, the div moves down a bit as a result. How do I make the div stay in the same place and extend equally to all sides without moving the div down a bit? Here is the code I have used so far.

html, body {
    padding: 0;
    color: #000;
    font-size:14px;
    background-color:#e8e8e8;
    vertical-align: middle;
    font-family:arial,sans-serif,verdana
}
div#bg1 {
    display: inline-block;
    width: 100%;
    margin: 50px 0px;
    text-align: center;
}
.div1{
    display: inline-block;
    width: 30%;
    background-color: #FFF;
    color: #000;
    font-size: 14px;
    font-weight: bold;
    border-radius: 15px;
    border: 15px solid transparent;
}

.div1:hover{
    display: inline-block;
    width: 30%;
    background-color: #FFF;
    color: #000;
    font-size: 14px;
    font-weight: bold;
    padding: 5px;
    border-radius: 15px;
    cursor: pointer;
    transition: 0.15s;
}

<html>
  <head>
  </head>
  <body>
    <div id='bg1'>
      <div  align="center">This is a test</div>
    </div>
  </body>
</html>

As you can see, the top line stays the same, which moves you the entire div down. Where do I have a thinking error?

CodePudding user response：

add a minus margin to hover state:

html, body {
    padding: 0;
    color: #000;
    font-size:14px;
    background-color:#e8e8e8;
    vertical-align: middle;
    font-family:arial,sans-serif,verdana
}
div#bg1 {
    display: inline-block;
    width: 100%;
    margin: 50px 0px;
    text-align: center;
}
.div1{
    display: inline-block;
    width: 30%;
    background-color: #FFF;
    color: #000;
    font-size: 14px;
    font-weight: bold;
    border-radius: 15px;
    border: 15px solid transparent;
}

.div1:hover{
    display: inline-block;
    width: 30%;
    background-color: #FFF;
    color: #000;
    font-size: 14px;
    font-weight: bold;
    padding: 5px;
    margin: -5px;
    border-radius: 15px;
    cursor: pointer;
    transition: 0.15s;
}

<html>
  <head>
  </head>
  <body>
    <div id='bg1'>
      <div  align="center">This is a test</div>
    </div>
  </body>
</html>