CSS

inner border css

div{
    -webkit-box-shadow:inset 0px 0px 0px 10px #f00;
    -moz-box-shadow:inset 0px 0px 0px 10px #f00;
    box-shadow:inset 0px 0px 0px 10px #f00;
}

add inner border css

.inner-border {
  border: 4px solid #e5621a;
  border-radius: 9px;
  box-shadow: inset 0px 0px 0px 1px white;
  box-sizing: border-box; /* Include padding and border in element's width and height */
}
//make sure background and border color are same with different box-shadow.
<button className="bg-[#e5621a] p-4 inner-border">Inner border</button>

inner border css

div {
    box-sizing: border-box;
    -moz-box-sizing: border-box;
    -webkit-box-sizing: border-box;
    width: 100px;
    height: 100px;
    border: 20px solid #f00;
    background: #00f;
    margin: 10px;
}

div + div {
    border: 10px solid red;
}