Creating a triangle centered below all but last list items

I want to create a triangle below the center of each li element but not the last one.

html

<ul class="steps-ul">
  <li> Step 1: Hardware Mounting </li>
  <li> Step 2: Hardware Connection </li>
  <li> Step 3: Devices Connection </li>
  <li> Step 4: Initial Test </li>
</ul>

css

.steps-ul {
  list-style-type: none;
  width: 500px;
  text-align: center;
}

.steps-ul li:nth-child(odd) {
  background-color:#efefef;
}
.steps-ul li:nth-child(odd)::after {
  border-top: 20px solid #efefef;
}
.steps-ul li {
  margin: 20px;
  padding: 10px;
  font-size: 1.5em;
  background-color:#d7d7d7;
}
.steps-ul li::after {
  position: absolute;
  left: 270px;
  margin-top: 30px;
  width: 0; 
  height: 0; 
  border-left: 20px solid transparent;
  border-right: 20px solid transparent;
  border-top: 20px solid #d7d7d7;
}

Heres a screenshot of what i would like to accomplish

I attempted using the ::after psuedo element within css but no results.

Your ::after selector is missing a content property, which is required for pseudo elements to be displayed.

.steps-ul li::after {
  content: " ";
  width: 0;
  height: 0;
  border-left: 50px solid transparent;
  border-right: 50px solid transparent;
  border-bottom: 100px solid red;
}

Copied the triangle code from this question.

As for not adding the triangle to the last element, you can use the :not(:last-child) selector.