flex-basis

                                
<div id="wrap">
    <div class="flexArea fe-basis-d">
        <div class="flexItem"></div>
    </div>

    <div class="flexArea fe-basis">
        <div class="flexItem"></div>
    </div>

    <div class="flexArea fe-basis fd-col">
        <div class="flexItem"></div>
    </div>
</div>

                                        
#wrap{padding: 50px; box-sizing: border-box;
    .flexArea{display: flex;
        .flexItem{display: flex; width: 200px; height: 200px; max-width: 200px; font-size: 16px; font-family: 'Noto Sans'; 
        color: #fff; background-color: #000;
            +.flexItem{margin-left: 10px;}
        }
        &.fe-basis-d .flexItem{flex-basis: auto;}
        &.fe-basis .flexItem{flex-basis: 600px;}
    }
}

                                        
#wrap{
    padding: 50px;
    -webkit-box-sizing: border-box;
    box-sizing: border-box;
}

#wrap .flexArea {
    display: -webkit-box;
    display: -ms-flexbox;
    display: flex;
}

#wrap .flexArea .flexItem {
    display: -webkit-box;
    display: -ms-flexbox;
    display: flex;
    width: 200px;
    height: 200px;
    max-width: 200px;
    font-size: 16px;
    font-family: 'Noto Sans';
    color: #fff;
    background-color: #000;
}

#wrap .flexArea .flexItem + .flexItem {
    margin-left: 10px;
}

#wrap .flexArea.fe-basis-d .flexItem {
    -ms-flex-preferred-size: auto;
        flex-basis: auto;
}

#wrap .flexArea.fe-basis .flexItem {
    -ms-flex-preferred-size: 600px;
        flex-basis: 600px;
}

Esc 혹은 우측 상단 X 버튼을 눌러 결과창을 닫을 수 있습니다.