FlexBox

Fluid CSS

HTML

<div class="wrapper">
<div class="fluid">2. Fluid Center</div>
    <div class="fixed">1. Fixed Right</div>
    
    <div class="fixed">3. Fixed Left</div>
</div>

CSS

.wrapper {
    margin:10px;
    height:40px;
    display: flex;
}
.wrapper div {
    margin: auto;
    min-width:100px;
    border:1px solid yellow;
    padding: 10px 0;
    text-align: center;
}
.fixed {
    width:100px;
    background:green;
}
.fluid {
    flex: 1;
    background:red;
    border-left:none !important;
    border-right:none !important;
}