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HTML

              
                <p class="warning">
  A tabbed component that turns into an accordion when tabs run out of space, using CSS and vanilla JavaScript. <a class="more" href="https://www.gsarigiannidis.gr/tabs-on-desktop-accordion-on-mobile/" target="_blank">Read more</a>
</p>
<h2>Bigger tabs</h2>
<article class="ootb-tabcordion">
	<div class="ootb-tabcordion--tabs" role="tablist" aria-label="TabCordion">
    <button class="tab is-active" role="tab" aria-selected="true" aria-controls="tab1-tab" id="tab1">Tab 1 with big text</button>
    <button class="tab" role="tab" aria-selected="false" aria-controls="tab2-tab" id="tab2" tabindex="-1">Tab 2 with big text</button>
    <button class="tab" role="tab" aria-selected="false" aria-controls="tab3-tab" id="tab3" tabindex="-1">Tab 3 with big text</button>
	</div>
	<section id="tab1-tab" class="ootb-tabcordion--entry is-active" data-title="Tab 1 with big text" tabindex="0" role="tabpanel" aria-labelledby="tab1">
		<div class="ootb-tabcordion--entry-container">
			<div class="ootb-tabcordion--entry-content">
				<p>A simple solution for having tabbed content on a large screen but turn it into accordion on a smaller
					one when the time is right. Just resize your screen to see the tabbed interface transforming into an
					accordion.</p>
				<p>In order to keep the HTML as clean as possible, without duplicating elements, we use element
					attributes as CSS content to display the accordion tabs. <a class="more" href="https://www.gsarigiannidis.gr/tabs-on-desktop-accordion-on-mobile/" target="_blank">Read more</a></p>
			</div>
		</div>
	</section>
	<section id="tab2-tab" class="ootb-tabcordion--entry" data-title="Tab 2 with big text" tabindex="-1" role="tabpanel" aria-labelledby="tab2">
		<div class="ootb-tabcordion--entry-container">
			<div class="ootb-tabcordion--entry-content">
        <p>Tab 2 content. Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Donec odio. Quisque volutpat
				mattis eros. Nullam malesuada erat ut turpis. Suspendisse urna nibh, viverra non, semper suscipit,
				posuere a, pede. Nullam malesuada erat ut turpis. Suspendisse urna nibh, viverra non, semper suscipit,
				posuere a, pede.</p>
			</div>
		</div>
	</section>
	<section id="tab3-tab" class="ootb-tabcordion--entry" data-title="Tab 3 with big text" tabindex="-1" role="tabpanel" aria-labelledby="tab3">
		<div class="ootb-tabcordion--entry-container">
			<div class="ootb-tabcordion--entry-content">
        <p>Tab 3 content. Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Donec odio. Quisque volutpat
				mattis eros. Nullam malesuada erat ut turpis. Suspendisse urna nibh, viverra non, semper suscipit,
				posuere a, pede. Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Donec odio. Quisque volutpat
				mattis eros. Nullam malesuada erat ut turpis. Suspendisse urna nibh, viverra non, semper suscipit,
				posuere a, pede. Lorem ipsum dolor sit amet, consectetuer adipiscing elit. Donec odio. Quisque volutpat
				mattis eros. Nullam malesuada erat ut turpis. Suspendisse urna nibh, viverra non, semper suscipit,
				posuere a, pede.</p>
			</div>
		</div>
	</section>
</article>
              
            
!

CSS

              
                p.warning {
  text-align: center;
  line-height: 2;
  margin-bottom: 2rem;
  a {
    background: #3bacff;
    color: #fff;
    padding: .2rem .7rem;
    border-radius: 3px;
    white-space: nowrap;
    text-decoration: none;
    &.more {
      background: #45ba04;
    }
  }
}

$color__tab: #444;
$color__tab-active: #3bacff;
$background__main: #dce2e2;
$color__light: #fff;
$width__max: 680px;
$padding: 1rem;
$border__radius: 3px;
$lighten__level: 6;
$darken__level: 6;
$font__family: 'Roboto', sans-serif;
$font__weight: 300;
$font__size: 16px;
@mixin tab-active() {
  background: $color__tab-active;
  color: $color__light;
}

* {
  box-sizing: border-box;
}

body {
  padding: $padding;
  background: $background__main;
  color: $color__tab;
  font-family: $font__family;
  font-weight: $font__weight;
}

p {
  margin-top: 0;
  line-height: 1.6;
}

h2 {
  margin: 0 auto;
  text-align: center;
  font-weight: 300;
}

.ootb-tabcordion {
  background: $color__light;
  box-shadow: 1px 1px 6px rgba(0, 0, 0, 0.2);
  max-width: $width__max;
  padding: $padding;
  margin: $padding auto $padding*4 auto;
  border-radius: $border__radius;
  &.has-tabs {
    .ootb-tabcordion--tabs {
      opacity: 1;
      height: auto;
      visibility: visible;
    }

    .ootb-tabcordion--entry {
      min-height: 0;

      &::before {
        display: none;
      }

      &.is-active {
        .ootb-tabcordion--entry-content {
          opacity: 1;
          transition: opacity 400ms ease-in-out;
        }
      }
      .ootb-tabcordion--entry-content {
        opacity: 0;
        transition: opacity 400ms ease-in-out;
      }
    }

   
  }
}

.ootb-tabcordion--tabs {
  opacity: 0;
  height: 0;
  visibility: hidden;
	display: flex;
	flex-flow: wrap;
	margin: 0;
	list-style: none;
	padding: 0;

	.tab {
	  display: block;
	  background: $color__tab;
	  color: #fff;
	  padding: #{$padding/2} $padding;
	  border-radius: $border__radius;
    font-size: $font__size;
    font-weight: $font__weight;
    font-family: $font__family;
	  margin: 0 0 1px 0;
    border: none;
    border-right: 1px solid #fff; // Set the disstance with border instead of margin, for more accurate JS calculation of the width
    cursor: pointer;
	  &:hover,
    &:focus {
		  background: lighten($color__tab, $lighten__level);
      outline: none;
	  }

	  &.is-active {
		  background: $color__tab-active;
      &:hover,
      &:focus {
        background: darken($color__tab-active, $darken__level);
      }
	  }
  }
}

.ootb-tabcordion--entry {
  overflow: hidden;
  &::before {
    position: relative;
    content: attr(data-title);
    cursor: pointer;
    z-index: 1;
    background: $color__tab;
    color: #fff;
    padding: #{$padding/2} $padding;
    display: block;
    border-radius: $border__radius;
  }

  &:hover,
  &:focus {
    outline: none;
    &::before {
      background: lighten($color__tab, $lighten__level);
    }
  }

  &.is-active {
    .ootb-tabcordion--entry-content {
      margin-top: 0;
      height: auto;
      opacity: 1;
      transition: margin 400ms ease-out -100ms;
    }
    
    &::before {
      background: $color__tab-active;
    }
    &:hover,
    &:focus {
      &::before {
        background: darken($color__tab-active, $darken__level);
      }
    }
  }
}

.ootb-tabcordion--entry-container {
  overflow: hidden;
  margin-bottom: 1px;
}

.ootb-tabcordion--entry-content {
  position: relative;
  margin-top: -100%;
  height: 0;
  opacity: 0;
  transition: margin 500ms ease-in;
  padding: $padding;
  a.more {
    color: $color__tab;
    &:hover {
      color: $color__tab-active;
    }
  }
}
              
            
!

JS

              
                (function () {
	'use strict';

  const keyboardSupport = function(container, hasTabs) {
    const tablist = container.querySelectorAll('[role="tablist"]')[0];
    let tabs;
    let panels;

    const generateArrays = function() {
      panels = container.querySelectorAll('[role="tabpanel"]');
      tabs = container.querySelectorAll('[role="tab"]');
    };
    
    generateArrays();

    // For easy reference
    const keys = {
      end: 35,
      home: 36,
      left: 37,
      up: 38,
      right: 39,
      down: 40,
      delete: 46,
      enter: 13,
      space: 32
    };

    // Add or subtract depending on key pressed
    const direction = {
      37: -1,
      38: -1,
      39: 1,
      40: 1
    };

    // Deactivate all tabs and tab panels
    const deactivateTabs = function() {
      for (let t = 0; t < tabs.length; t++) {
        tabs[t].setAttribute('tabindex', '-1');
        tabs[t].setAttribute('aria-selected', 'false');
      }
    };
    
    // Activates any given tab panel
    const activateTab = function(tab, setFocus) {
      setFocus = setFocus || true;
      // Deactivate all other tabs
      deactivateTabs();

      // Remove tabindex attribute
      tab.removeAttribute('tabindex');

      // Set the tab as selected
      tab.setAttribute('aria-selected', 'true');

      // Set focus when required
      if (setFocus) {
        tab.focus();
      }
    };
    
    const triggerTabClick = function(e) {
      const clickedId = e.target.getAttribute('id');
      if(clickedId) {
        const clickedTab = container.querySelector('[aria-controls="' + clickedId + '"]');
        clickedTab.click();
         document.getElementById(clickedId).scrollIntoView({
          behavior: 'smooth'
        });
      }
    };
    
    const accordionClickEventListener = function(event) {
      triggerTabClick(event);
    };
    
    // When a tab is clicked, activateTab is fired to activate it
    const clickEventListener = function(event) {
       const tab = event.target;
        activateTab(tab, false);
    };
    
    // Make a guess
    const focusFirstTab = function() {
      const target = hasTabs ? tabs : panels;
      target[0].focus();
    };

    // Make a guess
    const focusLastTab = function() {
      const target = hasTabs ? tabs : panels;
      target[target.length - 1].focus();
    };
    
    // Either focus the next, previous, first, or last tab
    // depending on key pressed
    const switchTabOnArrowPress = function(event) {
      const pressed = event.keyCode;

      if (direction[pressed]) {
        const target = event.target;
        const targetElems = hasTabs ? tabs : panels;
        if (target.index !== undefined) {
          if (targetElems[target.index + direction[pressed]]) {
            targetElems[target.index + direction[pressed]].focus();
          }
          else if (pressed === keys.left || pressed === keys.up) {
            focusLastTab();
          }
          else if (pressed === keys.right || pressed == keys.down) {
            focusFirstTab();
          }
        }
      }
    };
    
    // When a tablist's aria-orientation is set to vertical,
    // only up and down arrow should function.
    // In all other cases only left and right arrow function.
    const determineOrientation = function(event) {
      const key = event.keyCode;
      const vertical = tablist ? tablist.getAttribute('aria-orientation') === 'vertical' : null;
      let proceed = false;

      if (vertical || !hasTabs) {
        if (key === keys.up || key === keys.down) {
          event.preventDefault();
          proceed = true;
        }
      }
      else {
        if (key === keys.left || key === keys.right) {
          proceed = true;
        }
      }

      if (proceed) {
        switchTabOnArrowPress(event);
      }
    };
    
    // Handle keydown on tabs
    const keydownEventListener = function(event) {
      const key = event.keyCode;
      switch (key) {
        case keys.end:
          event.preventDefault();
          // Activate last tab
          focusLastTab();
          break;
        case keys.home:
          event.preventDefault();
          // Activate first tab
          focusFirstTab();
          break;

          // Up and down are in keydown
          // because we need to prevent page scroll >:)
          case keys.up:
          case keys.down:
          determineOrientation(event);
          break;
      }
    };

    // Handle keyup on tabs
    const keyupEventListener = function(event) {
      const key = event.keyCode;
      switch (key) {
        case keys.left:
        case keys.right:
          determineOrientation(event);
          break;
        case keys.enter:
        case keys.space:
          if(hasTabs) {
            activateTab(event.target);
          } else {
            triggerTabClick(event);
          }
          break;
      }
    };

    const addListeners = function(index) {
      const target = hasTabs ? tabs[index] : panels[index];
      tabs[index].addEventListener('click', clickEventListener);
      if(target) {
         if(!hasTabs) {
          target.addEventListener('click', accordionClickEventListener);
        }
        target.addEventListener('keydown', keydownEventListener);
        target.addEventListener('keyup', keyupEventListener);
        // Build an array with all tabs (<button>s) in it
        target.index = index;
      }    
    };

    // Bind listeners
    for (let i = 0; i < tabs.length; ++i) {
      addListeners(i);
    }
   
    // Accordion mode
    if(!hasTabs) {
      for (const panel of panels) {
        panel.onclick = function(e) {
          triggerTabClick(e);
        };
      }
    }   
};
  
	const toggleClass = function (otherElems, thisELem, className = 'is-active') {
		for (const otherElem of otherElems) {
			otherElem.classList.remove(className);
		}
		thisELem.classList.add(className);
	};
  
  const toggleVerticalTabs = function (tabContainer, tabs, items, item) {
    item.onclick = function (e) {
				const currId = item.getAttribute('id');
				const tab = tabContainer.querySelector('.ootb-tabcordion--tabs [aria-controls="' + currId + '"]');
				toggleClass(tabs, tab);
				toggleClass(items, item);
			};
  };
  
	const toggleTabs = function (tabContainer) {
		const tabs = tabContainer.querySelectorAll('.ootb-tabcordion--tabs .tab');
		const items = tabContainer.querySelectorAll('.ootb-tabcordion--entry');
		for (const tab of tabs) {
      tab.onclick = function() {
        const target = tab.getAttribute('aria-controls');
        const content = document.getElementById(target);
        toggleClass(tabs, tab);
        toggleClass(items, content);
      };
		}
		for (const item of items) {
			toggleVerticalTabs(tabContainer, tabs, items, item);
		}
	};

  const hasTabs = function(container) {
    return container.classList.contains('has-tabs');
  };
  
	const modeSwitcher = function (tabContainer, containerWidth) {
		const tabs = tabContainer.querySelectorAll('.tab');
    const container = tabs[0].closest('.ootb-tabcordion');
		let totalW = 0;
		for (const tab of tabs) {
			totalW += tab.offsetWidth;
		}
		if (totalW >= containerWidth) {
			container.classList.remove('has-tabs');
		} else {
			container.classList.add('has-tabs');
		}
    keyboardSupport(tabContainer, hasTabs(container));
	};
	
	const resizeObserver = new ResizeObserver(entries => {
		for (let entry of entries) {
			modeSwitcher(entry.target, entry.contentRect.width);
		}
	});

	const tabContainers = document.querySelectorAll('.ootb-tabcordion');
	for (const tabContainer of tabContainers) {
		const tabList = tabContainer.querySelector('.ootb-tabcordion--tabs');
		resizeObserver.observe(tabList);
		toggleTabs(tabContainer);
    keyboardSupport(tabContainer, hasTabs(tabContainer));
	}
})();
              
            
!
999px

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