First of all, the height of body, html and container (see element with class 'container') has to have height: 100%;
In this solution I have used flex box. It is supported by all modern browsers and IE11.
It's necessary to add the following properties to container:
display: flex;
flex-direction: column; /*the flex items are placed in column, by default it is in row*/
To move footer to bottom, just add to flex item
margin-top: auto; /* it grabs all free space between flex items and put it before this flex item */
html, body {
height: 100%;
}
.container {
height: 100%;
background-color: green;
display: flex;
flex-direction: column;
}
.header {
height: 20%;
background-color: yellow;
}
.content {
background-color: white;
}
.footer {
min-height: 20%;
background-color: blue;
margin-top: auto;
}
<div class="container">
<div class="header">Header</div>
<div class="content">It's content</div>
<div class="footer">Footer in bottom</div>
</div>