arasome

.header-wrap {
    width: 100%;
    height: 100px;
}
.footer-wrap {
    width: 100%;
    height: 50px;    
}
.container {
    display: table;
}
.container > .sidebar,
.container > .content {
    vertical-align: top;
    display: table-cell;    
}
.container > .sidebar{
    width: 30%;
}
.container > .content{
    width: 70%;
}

<div class="header-wrap"></div>
<div class="container">
    <div class="sidebar"></div>
    <div class="content"></div>
</div>
<div class="footer-wrap"></div>