<div class="tabs">
  <input type="radio" name="tabs" id="tabone" checked="checked">
  <label for="tabone">Tab One</label>
  <div class="tab">
    <h1>Tab One Content</h1>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
  </div>
  
  <input type="radio" name="tabs" id="tabtwo">
  <label for="tabtwo">Tab Two</label>
  <div class="tab">
    <h1>Tab Two Content</h1>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit, sed do eiusmod tempor incididunt ut labore et dolore magna aliqua. Ut enim ad minim veniam, quis nostrud exercitation ullamco laboris nisi ut aliquip ex ea commodo consequat. Duis aute irure dolor in reprehenderit in voluptate velit esse cillum dolore eu fugiat nulla pariatur. Excepteur sint occaecat cupidatat non proident, sunt in culpa qui officia deserunt mollit anim id est laborum.</p>
  </div>
  
  <input type="radio" name="tabs" id="tabthree">
  <label for="tabthree">Tab Three</label>
  <div class="tab">
    <h1>Tab Three Content</h1>
    <p>Lorem ipsum dolor sit amet, consectetur adipisicing elit.</p>
  </div>
</div>

/**
 * Tabs
 */
.tabs {
  display: flex;
  flex-wrap: wrap; // make sure it wraps
}
.tabs label {
  order: 1; // Put the labels first
  display: block;
  padding: 1rem 2rem;
  margin-right: 0.2rem;
  cursor: pointer;
  background: #90CAF9;
  font-weight: bold;
  transition: background ease 0.2s;
}
.tabs .tab {
  order: 99; // Put the tabs last
  flex-grow: 1;
  width: 100%;
  display: none;
  padding: 1rem;
  background: #fff;
}
.tabs input[type="radio"] {
  display: none;
}
.tabs input[type="radio"]:checked + label {
  background: #fff;
}
.tabs input[type="radio"]:checked + label + .tab {
  display: block;
}

@media (max-width: 45em) {
  .tabs .tab,
  .tabs label {
    order: initial;
  }
  .tabs label {
    width: 100%;
    margin-right: 0;
    margin-top: 0.2rem;
  }
}

/**
 * Generic Styling
*/
body {
  background: #eee;
  min-height: 100vh;
  box-sizing: border-box;
  padding-top: 10vh;
  font-family: "HelveticaNeue-Light", "Helvetica Neue Light", "Helvetica Neue", Helvetica, Arial, "Lucida Grande", sans-serif; 
  font-weight: 300;
  line-height: 1.5;
  max-width: 60rem;
  margin: 0 auto;
  font-size: 112%;
}

/**
 * Responsive pure CSS tabs & accordion
 * Without position absolute & with a selected state
 */

/**

A lot of CSS tabs need either the tab content or labels to be position absoluted, or sacrifice the selected state on the tabs.

This uses flexbox and order to have both.

It also allows you to drop down to an accordion when on mobile.
*/