<!-- markup structure
nav, a wrapping container for a series of link elements
  a, each anchor link element nesting an SVG icon and a span describing the link
-->
<nav>
  <a class="active" href="#">
    <svg viewBox="0 0 100 100">
      <g transform="translate(10 5) scale(0.8 0.9)">
        <path d="M 0 30 v 70 h 100 v -70 l -50 -30 z" stroke="currentColor" stroke-width="10" fill="none"
          stroke-linejoin="round" stroke-linecap="round" />
      </g>
    </svg>
    <span>
      Home
    </span>
  </a>

  <a href="#">
    <svg viewBox="0 0 100 100">
      <g transform="translate(5 5) scale(0.9 0.9)">
        <path d="M 50 35 a 20 20 0 0 1 50 0 q 0 25 -50 60 q -50 -35 -50 -60 a 25 25 0 0 1 50 0" stroke="currentColor"
          stroke-width="10" fill="none" stroke-linejoin="round" stroke-linecap="round" />
      </g>
    </svg>
    <span>
      Likes
    </span>
  </a>

  <a href="#">
    <svg viewBox="0 0 100 100">
      <g transform="translate(5 5) scale(0.9 0.9)">
        <circle cx="45" cy="38" r="38" stroke="currentColor" stroke-width="10" fill="none" />
        <line x1="66" y1="65" x2="100" y2="100" stroke="currentColor" stroke-width="10" />
      </g>
    </svg>
    <span>
      Search
    </span>
  </a>

  <a href="#">
    <svg viewBox="0 0 100 100">
      <g transform="translate(5 5) scale(0.9 0.9)">
        <circle cx="50" cy="35" r="18" stroke="currentColor" stroke-width="10" fill="none" />
        <rect x="15" y="75" width="70" height="50" rx="25" stroke="currentColor" stroke-width="10" fill="none" />
      </g>
    </svg>
    <span>
      Profile
    </span>
  </a>
</nav>
@import url("https://fonts.googleapis.com/css?family=Open+Sans:700");

* {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}

/* by default include the background of the option for the home navigation */
body {
  background: #5b37b7;
  color: #010101;
  /* center in the viewport */
  min-height: 100vh;
  display: grid;
  place-items: center;
  font-family: "Open Sans", sans-serif;
  /* transition for the change in bg color */
  transition: background 0.2s ease-out;
}

/* display the anchor link side by side  */
nav {
  display: flex;
  background: #fff;
  /* considerable whitespace surrounding the navigation's items */
  padding: 2rem 3.15rem;
  border-radius: 0 0 30px 30px;
  box-shadow: 0 1px 15px rgba(0, 0, 0, 0.1);
}

/* remove default style and slightly separate the anchor links from one another */
a {
  color: inherit;
  text-decoration: none;
  margin: 0 0.2rem;
  /* display the svg icon and span elements side by side, vertically aligned */
  display: flex;
  align-items: center;
  /* include padding for the background applied on the active item */
  padding: 0.75rem 1.25rem;
  border-radius: 30px;
  /* position relative for the pseudo element */
  position: relative;
  /* custom properties for the colors picked up by the elements when clicked (and updated for each link in the script) */
  --hover-bg: #5b37b720;
  --hover-c: #5b37b7;
}

/* include considerable negative margin to have the svg icon overlapping with the span element */
a svg {
  margin-right: -2.5rem;
  width: 28px;
  height: 28px;
  pointer-events: none;
  /* transition for the change in margin */
  transition: margin 0.2s ease-out;
}
/* by default hide the span element */
a span {
  opacity: 0;
  visibility: hidden;
  font-size: 0.9rem;
  margin-left: 0.9rem;
}
/* include with a pseudo element relative to the anchor link a circle, with a fixed with and height */
a:before {
  position: absolute;
  content: "";
  top: 50%;
  left: 0;
  width: 70px;
  height: 70px;
  border-radius: 50%;
  /* positioned to the left of the anchor link and scaled to 0 */
  transform: translate(0%, -50%) scale(0);
  visibility: visible;
  opacity: 1;
}
/* when active */
/* specify the colors dictated by the custom properties */
a.active {
  background: var(--hover-bg);
  color: var(--hover-c);
}
/* using the color specified by the then updated custom property show the circle of the pseudo element increasing its size and highlighting it momentarily */
a.active:before {
  background: var(--hover-c);
  opacity: 0;
  visibility: hidden;
  transform: translate(0%, -50%) scale(2);
  /* transition only when the class is applied */
  transition: all 0.4s ease-out;
}
/* remove the margin applied to the svg to make it overlay atop the anchor link */
a.active svg {
  margin-right: 0;
}
/* show the span element */
a.active span {
  visibility: visible;
  opacity: 1;
  transition: all 0.2s ease-out;
}

/* on smaller viewports show the navigation bar on the side, attached to the left of the screen */
@media (max-width: 500px) {
  nav {
    flex-direction: column;
    justify-self: start;
    border-radius: 0 30px 30px 0;
    padding: 2rem 1.15rem 2rem 0.75rem;
  }
  /* change the margin separating the anchor link elements now dividing the elements vertically */
  nav a {
    margin: 0.5rem 0;
  }
  /* remove the negative margin from the svg elements, as the width is to be taken in full */
  nav svg {
    margin: 0;
  }
}
// array describing the options of the navigation elements
// specifying the lower case option and the matching color
const navigationOptions = [
  {
    name: 'home',
    color: '#5B37B7'
  },
  {
    name: 'likes',
    color: '#C9379D'
  },
  {
    name: 'search',
    color: '#E6A919'
  },
  {
    name: 'profile',
    color: '#1892A6'
  }
];

// target all anchor link elements
const links = document.querySelectorAll('nav a');

// function called in response to a click event on the anchor link
function handleClick(e) {
  // prevent the default behavior, but most importantly remove the class of .active from those elements with it
  e.preventDefault();
  links.forEach(link => {
    if (link.classList.contains('active')) {
      link.classList.remove('active');
    }
  });

  // retrieve the option described the link element
  const name = this.textContent.trim().toLowerCase();
  // find in the array the object with the matching name
  // store a reference to its color
  const { color } = navigationOptions.find(item => item.name === name);

  // retrieve the custom property for the --hover-c property, to make it so that the properties are updated only when necessary
  const style = window.getComputedStyle(this);
  const hoverColor = style.getPropertyValue('--hover-c');
  // if the two don't match, update the custom property to show the hue with the text and the semi transparent background
  if (color !== hoverColor) {
    this.style.setProperty('--hover-bg', `${color}20`);
    this.style.setProperty('--hover-c', color);
  }

  // apply the class of active to animate the svg an show the span element
  this.classList.add('active');
  // change the color of the background of the application to match
  document.querySelector('body').style.background = color;
}

// listen for a click event on each and every anchor link
links.forEach(link => link.addEventListener('click', handleClick));
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