flex

div a

div sub-a

i'm an element of sub-a

div b

div sub-b

i'm an element of sub-b

div c

div sub-c

div d

                    
                    <div class="flex-container">
                    
                        <div class="flex-item_2">div a
                            <div class="sub-a">div sub-a</div>
                            <p> i'm an element of sub-a</p>
                        </div>
                
                        <div class="flex-item_2">div b
                            <div class="sub-b">div sub-b</div>
                            <p> i'm an element of sub-b</p>
                        </div>
                        <div class="flex-item_2">div c
                            <div class="sub-c">div sub-c</div>
                        </div>
                        <div class="flex-item_2">div d
                        </div>
                    
                    <div class="flex-container">
                        <div>
                            <p>flex-container</p>
                            <code class="flex-item_3">
                            
                            <...>                           
                            </code>
                        </div>
                    </div>

.flex-container { 

                    display: flex; 

                    background-color: aqua; 

                }

                    
                      <div class="flex-container_2">
                      <div class="flex-container_3">
                        <div class="flex-item_3">
                          <img src="img/cities_1.webp" alt="" />
                        </div>
                        <div class="flex-item_3">
                          <img src="img/cities_2.webp" alt="" />
                        </div>
                        <div class="flex-item_3">
                          <img src="img/cities_3.webp" alt="" />
                        </div>
                      </div>
                  
                      <div class="flex-containter_2">
                        <div class="flex-item_2 code_html">
                          <pre>
                                  <code>

.flex-container_3 {
          display: flex;
          flex-direction: column;
          
          background-color: lightgreen;
          justify-content: center;
        }

          .flex-item_3 {
            background-color: darkblue;
            margin: 10px;
            padding: 10px;
          }