SOURCE

<div class="wrapper-1">
    <div class="left">100px</div>
    <div class="right">200px</div>
    <div class="middle">主体</div>
</div>

<div class="wrapper-2">
    <div class="left">左</div>
    <div class="middle">主体</div>
    <div class="right">右</div>
</div>

<div class="wrapper-3">
    <div class="left">左</div>
    <div class="middle">主体</div>
    <div class="right">右</div>
</div>

.wrapper-1{
    margin-bottom: 20px;
}
.wrapper-1 .left{
    float: left;
    width: 80px;
    height: 50px;
    padding: 10px;
    background-color: #dbdbdb;
    border-radius: 5px;
}
.wrapper-1 .middle{
    height: 50px;
    background-color: gray;
    margin: 0 210px 0 110px;
    padding: 10px;
    border-radius: 10px;
}
.wrapper-1 .right{
    float: right;
    width: 180px;
    height: 50px;
    background-color: #1bffff;
    padding: 10px;
    border-radius: 5px;
}

.wrapper-2{
    position: relative;
    height: 70px;
    margin-bottom: 20px;
}
.wrapper-2 .left{
    position: absolute;
    left: 0;
    width: 80px;
    height: 50px;
    padding: 10px;
    background-color: #dbdbdb;
    border-radius: 5px;
}   
.wrapper-2 .middle{
    position: absolute;
    top: 0;
    left: 0;
    right: 0;
    bottom: 0;
    height: 50px;
    background-color: gray;
    margin: 0 210px 0 110px;
    padding: 10px;
    border-radius: 10px;
    font-size: 16px;
}   
.wrapper-2 .right{
    position: absolute;
    right: 0;
    width: 180px;
    height: 50px;
    background-color: #1bffff;
    padding: 10px;
    border-radius: 5px;
}

.wrapper-3{
    display: flex;
}
.wrapper-3 .left{
    flex-shrink: 0;
    width: 80px;
    height: 50px;
    padding: 10px;
    background-color: #dbdbdb;
    border-radius: 5px;
}
.wrapper-3 .middle{
    flex: 1;
    height: 50px;
    background-color: gray;
    padding: 10px;
    margin: 0 10px;
    border-radius: 10px;
}
.wrapper-3 .right{
    flex-shrink: 0;
    width: 180px;
    height: 50px;
    background-color: #1bffff;
    padding: 10px;
    border-radius: 5px;
}