Radio Input Based Toggle Button Group With Pure CSS

A CSS only solution that converts a series of radio inputs into toggle buttons and groups them in an inline button group with gradients.

How to use it:

Create a series of radio buttons for the button group.

<div class="radio-pillbox">
  <radiogroup>
    <div>
      <input type="radio" name="radio-group" id="js" value="JavaScript" class="first">
      <label for="js" class="radio-label">JavaScript</label>
      </input>
    </div>
    <div>
      <input type="radio" name="radio-group" id="html5" value="HTML5">
      <label for="tricky">HTML5</label>
      </input>
    </div>
    <div>
      <input type="radio" name="radio-group" id="css" value="CSS3">
      <label for="css">CSS/CSS3</label>
      </input>
    </div>
    <div>
      <input type="radio" name="radio-group" id="angularjs" value="AngularJS">
      <label for="angularjs">AngularJS</label>
      </input>
    </div>
    <div>
      <input type="radio" name="radio-group" id="jquery" value="jQuery">
      <label for="jquery">jQuery</label>
      </input>
    </div>
    <div>
      <input type="radio" name="radio-group" id="rn" value="React Native" class="last">
      <label for="rn">React Native</label>
      </input>
    </div>
  </radiogroup>
</div>

The primary CSS/CSS3 rules for the button group.

.radio-label {
  width: 100%;
  margin-bottom: 1em;
  text-align: center;
}
.radio-pillbox {
  height: 5em;
  width: 100%;
  font-size: 1em;
  border: 0;
  border-radius: 75px;
  overflow: hidden;
  background: -webkit-linear-gradient(  100deg,  #0ef49b 0%,  #d2dc69 30%,  #faa04b 70%,  #ff5a64 100%  );
  background: -moz-linear-gradient(  100deg,  #0ef49b 0%,  #d2dc69 30%,  #faa04b 70%,  #ff5a64 100%  );
  background: -o-linear-gradient(  100deg,  #0ef49b 0%,  #d2dc69 30%,  #faa04b 70%,  #ff5a64 100%  );
  background: -ms-linear-gradient(  100deg,  #0ef49b 0%,  #d2dc69 30%,  #faa04b 70%,  #ff5a64 100%  );
  background: linear-gradient(  100deg,  #0ef49b 0%,  #d2dc69 30%,  #faa04b 70%,  #ff5a64 100%  );
  color: #000000;
  box-shadow: 0 2px 5px 0 rgba(0, 0, 0, 0.16), 0 2px 10px 0 rgba(0, 0, 0, 0.12);
}
.radio-pillbox radiogroup {
  height: 100%;
  width: 100%;
  display: flex;
}
.radio-pillbox radiogroup div {
  width: 100%;
  position: relative;
}
.radio-pillbox radiogroup div input {
  -webkit-appearance: inherit;
  width: 100%;
  height: 100%;
  transition: background 300ms ease-out;
  margin: 0;
  outline: 0;
  border-left: 1px solid rgba(0, 0, 0, 0.05);
}
.radio-pillbox radiogroup div input:checked {
  color: #5f6982;
  border: none;
  box-shadow: inset 0 10px 50px rgba(25, 25, 25, 0.1);
}
.radio-pillbox radiogroup .first {
  border-radius: 75px 0 0 75px;
  border-left: none;
}
.radio-pillbox radiogroup .last { border-radius: 0 75px 75px 0; }
.radio-pillbox radiogroup div label {
  position: absolute;
  top: 50%; /* top plus line-height centers text */
  line-height: 0;
  left: 0;
  width: 100%;
  height: 100%;
  text-align: center;
}
.radio-pillbox input:focus { outline: 0; }
.radio-pillbox label:after {
  content: "\2714";
  display: inline-block;
  -webkit-transform: scale(0);
  -moz-transform: scale(0);
  -o-transform: scale(0);
  -ms-transform: scale(0);
  transform: scale(0);
  -webkit-transition: margin 250ms cubic-bezier(0.6, -0.28, 0.735, 0.045) 100ms,  -webkit-transform 250ms cubic-bezier(0.895, 0.03, 0.685, 0.22);
  -moz-transition: margin 250ms cubic-bezier(0.6, -0.28, 0.735, 0.045) 100ms,  -moz-transform 250ms cubic-bezier(0.895, 0.03, 0.685, 0.22);
  -o-transition: margin 250ms cubic-bezier(0.6, -0.28, 0.735, 0.045) 100ms,  -o-transform 250ms cubic-bezier(0.895, 0.03, 0.685, 0.22);
  transition: margin 250ms cubic-bezier(0.6, -0.28, 0.735, 0.045) 100ms,  transform 250ms cubic-bezier(0.895, 0.03, 0.685, 0.22);
}
.radio-pillbox input:checked + label:after {
  margin-left: 12px;
  -webkit-transform: scale(1.25);
  -moz-transform: scale(1.25);
  -o-transform: scale(1.25);
  -ms-transform: scale(1.25);
  transform: scale(1.25);
  -webkit-transition: -webkit-transform 500ms  cubic-bezier(0.175, 0.885, 0.32, 1.275) 250ms,  margin 500ms,  -webkit-transform 500ms cubic-bezier(0.175, 0.885, 0.32, 1.275) 250ms;
  -moz-transition: -moz-transform 500ms cubic-bezier(0.175, 0.885, 0.32, 1.275)  250ms,  margin 500ms,  -moz-transform 500ms cubic-bezier(0.175, 0.885, 0.32, 1.275) 250ms;
  -o-transition: -o-transform 500ms cubic-bezier(0.175, 0.885, 0.32, 1.275)  250ms,  margin 500ms,  -o-transform 500ms cubic-bezier(0.175, 0.885, 0.32, 1.275) 250ms;
  transition: transform 500ms cubic-bezier(0.175, 0.885, 0.32, 1.275) 250ms,  margin 500ms, transform 500ms cubic-bezier(0.175, 0.885, 0.32, 1.275) 250ms;
}