<div class="icon">
  <svg width="100%" viewBox="0 0 24 24">
    <path d="M4,4H20A2,2 0 0,1 22,6V18A2,2 0 0,1 20,20H4C2.89,20 2,19.1 2,18V6C2,4.89 2.89,4 4,4M12,11L20,6H4L12,11M4,18H20V8.37L12,13.36L4,8.37V18Z"></path>
  </svg>
</div>
  
<div class="box">
  <div class="toggle" id="increase">
    <input type="checkbox">
    <span class="button"></span>
    <span class="label">+</span>
  </div>
  <div class="toggle" id="decrease">
    <input type="checkbox" checked>
    <span class="button"></span>
    <span class="label">–</span>
  </div>
</div>

@import url('https://fonts.googleapis.com/css?family=Gochi+Hand');

@import url(https://fonts.googleapis.com/css?family=Lato:700);

/* the cool stuff */

.icon {
  --number-var: 23;
}
.icon::before {
  counter-reset: number var(--number-var);
  content: counter(number);
}

/* the pretty stuff */

body {
  height: 100vh;
  background-color: #000;
  display: flex;
  align-items: center;
  justify-content: center;
  flex-direction: column;
  font-family: 'Gochi Hand', cursive;
  color: #fff;
}

.icon {
  position: relative;
  background-color: #fff;
  fill: #555;
  padding: 1.2rem;
  border-radius: 50%;
  width: 100px;
  height: 100px;
}

.icon::before {
  position: absolute;
  width: 35px;
  height: 35px;
  background-color: #9a59c2;
  border-radius: 50%;
  line-height: 1;
  box-sizing: border-box;
  padding: 0.6rem; /* optical adjustment */
  text-align: center;
  top: 0;
  right: -1%;
}

.box {
  display: flex;
  justify-content: center;
  align-items: center;
  min-width: 80vw;
  margin: 20px;
  font-family: 'Lato', sans-serif；
}

.toggle {
  margin: 4px;
  display: inline-block;
}

.toggle {
  box-shadow: inset 0 0 35px 5px rgba(0, 0, 0, 0.25), inset 0 2px 1px 1px rgba(255, 255, 255, 0.9), inset 0 -2px 1px 0 rgba(0, 0, 0, 0.25);
  border-radius: 8px;
  background: #ccd0d4;
  position: relative;
  height: 100px;
  width: 100px;
}
.toggle:before {
  box-shadow: 0 0 17.5px 8.75px #fff;
  border-radius: 118.3px;
  background: #fff;
  position: absolute;
  margin-left: -50.4px;
  margin-top: -50.4px;
  opacity: 0.2;
  content: "";
  height: 100.8px;
  width: 100.8px;
  left: 50%;
  top: 50%;
}
.toggle .button {
  -webkit-filter: blur(1px);
  -moz-filter: blur(1px);
  filter: blur(1px);
  transition: all 300ms cubic-bezier(0.23, 1, 0.32, 1);
  box-shadow: 0 15px 25px -4px rgba(0, 0, 0, 0.5), inset 0 -3px 4px -1px rgba(0, 0, 0, 0.2), 0 -10px 15px -1px rgba(255, 255, 255, 0.6), inset 0 3px 4px -1px rgba(255, 255, 255, 0.2), inset 0 0 5px 1px rgba(255, 255, 255, 0.8), inset 0 20px 30px 0 rgba(255, 255, 255, 0.2);
  border-radius: 96.32px;
  position: absolute;
  background: #ccd0d4;
  display: block;
  height: 80px;
  width: 80px;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
}
.toggle .label {
  transition: color 300ms ease-out;
  text-shadow: 1px 1px 3px #ccd0d4, 0 0 0 rgba(0, 0, 0, 0.8), 1px 1px 4px #fff;
  text-align: center;
  position: absolute;
  font-weight: 700;
  font-size: 42px;
  opacity: 0.9;
  height: 100%;
  width: 100%;
  color: rgba(0, 0, 0, 0.4);
  display: flex;
  align-items: center;
  justify-content: center;
}
.toggle input {
  opacity: 0;
  position: absolute;
  cursor: pointer;
  z-index: 1;
  height: 100%;
  width: 100%;
  left: 0;
  top: 0;
}
.toggle input:active ~ .button {
  box-shadow: 0 15px 25px -4px rgba(0, 0, 0, 0.4), inset 0 -8px 30px 1px rgba(255, 255, 255, 0.9), 0 -10px 15px -1px rgba(255, 255, 255, 0.6), inset 0 8px 25px 0 rgba(0, 0, 0, 0.4), inset 0 0 10px 1px rgba(255, 255, 255, 0.6);
}
.toggle input:active ~ .label {
  font-size: 40px;
  color: rgba(0, 0, 0, 0.45);
}
.toggle input:checked ~ .button {
  box-shadow: 0 15px 25px -4px rgba(0, 0, 0, 0.4), inset 0 -8px 25px -1px rgba(255, 255, 255, 0.9), 0 -10px 15px -1px rgba(255, 255, 255, 0.6), inset 0 8px 20px 0 rgba(0, 0, 0, 0.2), inset 0 0 5px 1px rgba(255, 255, 255, 0.6);
}
.toggle input:checked ~ .label {
  font-size: 40px;
  color: rgba(0, 0, 0, 0.4);
}

let styles = getComputedStyle(document.querySelector('.icon'));  
let increaseValue = Number(styles.getPropertyValue('--number-var')) + 1; 
let decreaseValue = Number(styles.getPropertyValue('--number-var')) - 1; 

document.getElementById('increase').addEventListener('click', function(e){
  document.querySelector('.icon').style.setProperty('--number-var', increaseValue++)
})

document.getElementById('decrease').addEventListener('click', function(e){
  document.querySelector('.icon').style.setProperty('--number-var', decreaseValue--)
})