<ol class="stepper">
   <li>Step A</li>
   <li class="active">Step B</li>
   <li>Step C</li>
   <li>Step D</li>
</ol>

<ol class="stepper">
   <li>Step A</li>
   <li>Step B</li>
   <li class="active">Step C</li>
   <li>Step D</li>
   <li>Step E</li>
</ol>

ol.stepper {
  --default-b: lightgrey;
  --default-c: black;
  --active-b: purple;
  --active-c: white;
  --circle: 3.5em; /* size of circle */
  --b: 5px; /* line thickness */
  
  display: flex;
  list-style: none;
  justify-content: space-between;
  background: 
    linear-gradient(var(--default-b) 0 0) no-repeat
    50% calc((var(--circle) - var(--b))/2)/100% var(--b);
  counter-reset: step;
  margin: 20px;
  padding: 0;
  font-size: 22px;
  font-weight: bold;
  counter-reset: step;
  overflow: hidden;
}
ol.stepper li {
  display: grid;
  place-items: center;
  gap: 5px;
  font-family: sans-serif;
  position: relative;
}
ol.stepper li::before {
  content: counter(step) " ";
  counter-increment: step;
  display: grid;
  place-content: center;
  aspect-ratio: 1;
  height: var(--circle);
  border: 5px solid #fff;
  box-sizing: border-box;
  background: var(--active-b);
  color: var(--active-c);
  border-radius: 50%;
  font-family: monospace;
  z-index: 1;
}
ol.stepper li.active ~ li::before{
  background: var(--default-b);
  color: var(--default-c);
}
ol.stepper li.active::after {
  content: "";
  position: absolute;
  height: var(--b);
  right: 100%;
  top: calc((var(--circle) - var(--b))/2);
  width: 100vw;
  background: var(--active-b);
}


@media (max-width: 600px) {
  ol.stepper {
   display: grid;
   gap: 20px;
  background: 
    linear-gradient(var(--default-b) 0 0) no-repeat
    calc((var(--circle) - var(--b))/2) 50%/ var(--b) 100%;
  }
  ol.stepper li {
    display: flex;
  }
  ol.stepper li.active::after {
    content: "";
    position: absolute;
    width: var(--b);
    bottom: 100%;
    left: calc((var(--circle) - var(--b))/2);
    top: auto;
    right: auto;
    height: 100vw;
    background: var(--active-b);
  }
}