Example with 2 columns of boxes that change to a single column on small screens

html

  <div class="my_root_container">

    <a href="/somepage">
      <div class="my_item_container">
        <div>
          <div class="my_item_image">
            <img src="my_image_default.png" alt="My Image" >
          </div>
          <div class="my_item_details">
            <p class="my_item_title">My Title</p>
          </div>
          <div style="clear:both"></div>
        </div>
      </div>
    </a>


    <a href="/somepage">
      <div class="my_item_container">
        <div>
          <div class="my_item_image">
            <img src="my_image_default.png" alt="My Image" >
          </div>
          <div class="my_item_details">
            <p class="my_item_title">My Title</p>
          </div>
          <div style="clear:both"></div>
        </div>
      </div>
    </a>

  </div>

css

/*---------------------------------------*/
/*---------------------------------------*/
/*----- RESPONSIVE COLUMNS OF BOXES -----*/
/*---------------------------------------*/
/*---------------------------------------*/
.my_root_container {
  clear: both;
}

.my_item_container {
  width: 240px;
  border: 1px solid #CCC;
  border-radius: 6px;
  margin-top: 16px;
  margin-right: auto;
  margin-left: auto;
  margin-bottom: 16px;
  padding-top: 6px;
  padding-right: 6px;
  padding-left: 6px;
  padding-bottom: 6px;
}

.my_item_image { 
  width: 226px;
  height: 120px;
  text-align: center;
  float: none;
  margin-left: auto;
  margin-right: auto;
}

.my_item_image img {
  width: 226px;
  height: 120px;
  object-fit: contain;
  margin-top: 0px;
  margin-right: auto;
  margin-left: auto;
  margin-bottom: 0px;
}

.my_item_details {
  overflow: hidden;
  padding: 0px 0px 0px 0px;
  position: relative;
  height: 50px;
}

.my_item_details, .my_item_details a, .my_item_details a:Hover, .my_item_details a:Visited {
  text-decoration: none;
}

.my_item_title {
  font-size: 18px;
  line-height: 140%;
  font-weight: bold;
  color: var(--odac-color-main1);
  margin: 6px 0px 0px 0px;
  padding: 0px 0px 6px 0px;
  text-align: center;
  width: 100%;
  
  position: absolute;
  top: 50%;
  transform: translateY(-54%);  /*For text can need 54%*/
}

/*CHANGE FROM MULTI COLUMN TO SINGLE COLUMN ON SMALL SCREENS */
@media only screen and (max-width: 800px) {
  /* When width is less than or equal to 800px */
  .my_root_container {
    width: 100%;
  }
  
  .my_item_container {
    float: none;
  }
}
@media only screen and (min-width: 801px) {
  /* When width is greater than or equal to 801px */
  .my_root_container {
    width: 560px;      /* (2 x odac_post_categories_item_container width) + (4 x odac_post_categories_item_container left right margins) */
    margin-right: auto;
    margin-left: auto;
  }
  
  .my_item_container {
    margin-right: 20px;
    margin-left: 20px;
    float: left;
  }
}