<wrapper>
  <div class="item">
    <p>Выберите число исполнителей</p>
    <div class="proggress"></div>
    <div class="item_wrapper">
      <span id="minus">-</span>
      <span id="number">1</span>
      <span id="plus">+</span>
    </div>
  </div>
</wrapper>

* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}
wrapper {
  display: block;
  padding: 10px;
}

.item {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 6px 4px;
  position: relative;
  overflow: hidden;
  mix-blend-mode: overlay;
  box-shadow: 0 0 5px #000;
}

.item p {
  position: relative;
  z-index: 10;
  font-size: 20px;
}

.item_wrapper {
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 0 5px #000;
  overflow: hidden;
  position: relative;
  z-index: 10;
  height: 30px;
}

.item_wrapper span {
  padding: 8px;
  font-size: 20px;
  background: #fff;
}

#number {
  display: inline-block;
  border-left: 1px solid #000;
  border-right: 1px solid #000;
  width: 40px;
  text-align: center;
}

.item,
.item_wrapper {
  border-radius: 6px;
}

#minus,
#plus {
  cursor: pointer;
  user-select: none;
}

#number {
  user-select: none;
}

.proggress {
  position: absolute;
  top: 0;
  left: 0;
  width: 10%;
  height: 100%;
  background: lightblue;
}

let num = document.getElementById("number");
let proggress = document.querySelector(".proggress");
minus.onclick = _minus;
plus.onclick = _plus;

function _plus() {
  num.innerHTML = Number(num.innerHTML) + 1;
  proggress.style.width = Number(num.innerHTML) * 10 + "%";
  if (num.innerHTML > 10) {
    num.innerHTML = 10;
  }
}

function _minus() {
  num.innerHTML = num.innerHTML - 1;
  proggress.style.width = num.innerHTML * 10 + "%";
  if (num.innerHTML < 0) {
    num.innerHTML = 0;
  }
}