.parent {
width:100%;
}
.child {
display:inline-block;
}<div class="parent">
<div class="child">child1</div>
<div class="child">child2</div>
<div class="child">child3</div>
</div>#logo {
background:#ccc;
height:50px;
width:100px;
border:1px solid;
}
#logo.s0,#logo.s1,#logo.s2 {
background:#ccc111;
}
#logo.s3,#logo.s4,#logo.s5 {
background:#111ccc;
}
#logo.s6,#logo.s7,#logo.s8 {
background:#c1c1c1;
}
#logo.s9,#logo.s10,#logo.s11 {
background:#1c1c1c;
}<div id="logo"></div>var date = new Date();
document.getElementById("logo").classList.add('s'+date.getMonth());