:placeholder-shown

/* Selects any element with an active placeholder */
:placeholder-shown {
  border: 2px solid silver;
}

<input placeholder="Type something here!">

input {
  border: 1px solid black;
  padding: 3px;
}

input:placeholder-shown {
  border-color: teal;
  color: purple;
  font-style: italic;
}

<input id="input1" placeholder="Name, Rank, and Serial Number">
<br><br>
<input id="input2" placeholder="Name, Rank, and Serial Number">

#input2:placeholder-shown {
  text-overflow: ellipsis;
}

<form id="test">
  <p>
    <label for="name">Enter Student Name:</label>
    <input id="name" placeholder="Student Name"/>
  </p>
  <p>
    <label for="branch">Enter Student Branch:</label>
    <input id="branch" placeholder="Student Branch"/>
  </p>
  <p>
    <label for="sid">Enter Student ID:</label>
    <input type="number" pattern="[0-9]{8}" title="8 digit ID" id="sid" class="studentid" placeholder="8 digit id"/>
  </p>
  <input type="submit"/>
</form>

input {
  background-color: #E8E8E8;
  color: black;
}

input.studentid:placeholder-shown {
  background-color: yellow;
  color: red;
  font-style: italic;
}