.box p{
    height: 30px;
    overflow: hidden;
}

.box a.readmore-btn{
    display: inline-block;
    color: #fff;
    background-color: #2196f3;
    text-decoration: none;
    padding: 10px 15px;
    border-radius: 8px;
}

.box.showContent p{
    height: auto;
}

.box.showContent a.readmore-btn{
    background-color: red;
}