.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%;
    text-align: center;
    padding: 10px 0;
    position: absolute;
    bottom: 0; 
}