Example code of CSS layout at both ends (using parent's negative margin)

<style>
        * {
            padding: 0px;
            margin: 0px;
            box-sizing: border-box;
        }
        
        .max-box {
            max-width: 1200px;
            margin: 0px auto;
        }
        
        .box {
            overflow: hidden;
            width: calc(100% + 20px);
            margin-left: -10px;
        }
        
        .inner {
            height: 100px;
            border: solid 1px red;
            float: left;
            margin-left: 10px;
            width: calc(((100% - 20px) - 10px * 3) / 4);
        }
        
        .max-box2 {
            max-width: 1200px;
            margin: 50px auto;
            border: solid 1px red;
            height: 200px;
        }
    </style>

 <div class="max-box2">

    </div>
    <div class="max-box">
        <div class="box">
            <div class="inner">

            </div>
            <div class="inner">

            </div>
            <div class="inner">

            </div>
            <div class="inner">

            </div>
        </div>
    </div>

x = 10px; i.e. the desired spacing y = 4 i.e. the desired number of rows Parent: width: calc(100% + (x * 2));
Child: width: calc(((100% - (x * 2)) - x * ( y - 1)) / y );