Pasted

* {
 box-sizing: border-box;
}
*:before,
*:after {
 box-sizing: border-box;
}
html,
body {
 height: 100%;
 position: relative;
}
.main-container {
 min-height: 100vh; /* will cover the 100% of viewport */
 overflow: hidden;
 display: block;
 position: relative;
 padding-bottom: 100px; /* height of your footer */
}
footer {
 position: absolute;
 bottom: 0;
 width: 100%;
}