title: How to fix the width of a flexbox item
body: <p>I want to add a responsive page that contains many cards of different widths , for example I want the first card have 520px, the second 300px etc.. but when I open them from mobile or and device it should be responsive
  someone advice me to use flexbox to be responsive but I use it and I don't Know how to responsive using it , I want to build a responsive page with css3 should I use flexbox ?</p>
  
  <p>when I minimise the browser there's no responsive page with this code : </p>
  
  <pre class="lang-css prettyprint-override"><code>#container-target {
    position: relative;
    background-color:#eeeeee; 
    max-width:590px;
    height:140px;
    border-radius:5px;
    display: flex;
    flex-direction: column;
  
  }
  
  .target {
    display: flex;
    flex-wrap: wrap;
    justify-content: space-between;
  }
  
  .button {
    margin-right: 20px;
  }
  
  #container-target .title {
    background-color:#111f35;
    color:white;
    height:35px;
    border-radius:5px;
  }
  
  
  </code></pre>
  
  <pre class="lang-html prettyprint-override"><code>&lt;!DOCTYPE html&gt;
  
  &lt;html&gt;
  
    &lt;head&gt;
  
      &lt;title&gt;Template&lt;/title&gt;
  
      &lt;meta charset="UTF-8" /&gt;
  
      &lt;link rel="stylesheet" href="style.css" /&gt;
  
    &lt;/head&gt;
  
    &lt;body&gt;
  
      &lt;div id="container-target"&gt;
  
        &lt;div class="title"&gt;
  
          CIBLAGE
  
        &lt;/div&gt;
  
        &lt;div class="body-target"&gt;
  
          &lt;p&gt;Envoyer à tout le monde ou cibler des utilisateurs.&lt;/p&gt; 
  
          &lt;div class="target"&gt;
  
              &lt;div class="radio"&gt;
  
                  &lt;input type="radio" name="radio" /&gt;Tout le monde
  
                &lt;/div&gt;
  
                &lt;div class="button"&gt;
  
                  &lt;button&gt;Créer un ciblage&lt;/button&gt;
  
                &lt;/div&gt;
  
          &lt;/div&gt;
  
  
        &lt;/div&gt;
  
      &lt;/div&gt;
  
    &lt;/body&gt;
  
  &lt;/html&gt;
  </code></pre>