.wrapper{
    min-height: 100vh;
    position: relative;/*←相対位置*/
    padding-bottom: 120px;/*←footerの高さ*/
    box-sizing: border-box;/*←全て含めてmin-height:100vhに*/
}

footer{
    width: 100%;
    background-color: #89c7de;
    color: #000;
    text-align: center;
    padding: 30px 0;

 position: absolute;/*←絶対位置*/
    bottom: 0; /*下に固定*/
}