html - Flex items in a row rendering at different widths -

i created 3 boxes using css flexbox in html chrome rendering boxes different sizes.

drag border of browser make view smaller.

thanks help!

codepen: https://codepen.io/labanino/pen/rganlp

body {    font-family: arial;    font-size: 2rem;    text-transform: uppercase;  }    .flex {    height: 200px;    display: flex;    flex-direction: row;  }    .flex>section {    flex: 1 1 auto;    display: flex;    justify-content: center;    flex-direction: column;    text-align: center;  }    .flex>section:nth-child(1) {    background: brown;    margin-right: 20px;    border: 1px solid #999;  }    .flex>section:nth-child(2) {    background: pink;    margin-right: 20px;    border: 1px solid #999;  }    .flex>section:nth-child(3) {    background: green;    margin-right: 0;    border: 1px solid #999;  }

<div class="flex">    <section>brown</section>    <section>pink</section>    <section>green</section>  </div>

don't use auto in flex property items. use 100%, , adapt width in flex box, , adjusts number of elements add (in case want add more 3).

.flex > section {   flex: 1 1 100%;     display: flex;   justify-content: center;   flex-direction: column;   text-align: center; } 

the reason they're different sizes because when use auto, bases width on content of box. that's why middle 1 isn't wide, because word 'pink' takes less space 'green'.