Div with height of 100% disappears as I scroll down through page when resizing

Question

I have a really quick question. I have set my side-bar div's height to 100% however whenever I resize the window so that the windows height is at the smallest and I scroll down the side-bar's height does not go to the bottom of the page. Here is a picture of what I am talking about

Here is my code:

<div class="wrapper">
      <div class="top-bar">
        <div class="search-input">
          <form>
            <div class="input-field">
              <input type="text" placeholder="Search user" name="userPost">
            </div>
          </form>
        </div>
      </div>
      <div class="side-bar">
        <div class="sub-title">
          <h3>ADMIN TOOLS<h3>
        </div>
        <div class="splitter"></div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="Dashboard" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-tachometer-alt fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="Ban Panel" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-ban fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="Warn Panel" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-exclamation-circle fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="Gift Panel" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-gift fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="User Info" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-user fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
        <div class="sub-title">
          <h3>NEWS TOOLS<h3>
        </div>
        <div class="splitter"></div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="New Post" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-file fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="Remove Post" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-trash fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
        <div class="sub-title">
          <h3>OTHER<h3>
        </div>
        <div class="splitter"></div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="Game Statistics" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-chart-line fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
      </div>
    </div>

CSS

*:focus {
  outline: none;
}

body {
  background-color: #F1F1FA;
  font-family: sans-serif;
  margin: 0;
  padding: 0;
}

.wrapper {
  height: 100vh;
}

.top-bar {
  display: flex;
  position: absolute;

  left: 17%;
  width: 83%;
  height: 50px;
  background-color: white;
  box-shadow: 0 2px 4px 0 rgba(0,0,0,0.10);
}

.search-input {
  align-self: center;
  margin-left: 10px;
}

.search-input form input[type="text"] {
  padding: 5px;
}

input[type="button"] {
  border: none;
  background-color: Transparent;
  outline: none;
  height: 20px;
  width: 92%;
  font-size: 13px;
  font-weight: regular;
  color: #B9B9B9;
  text-align: left;
}

.side-bar {
  display: flex;
  flex-direction: column;

  width: 17%;
  height: 100%;
  background-color: #272C32;
}

.sub-title {
  margin-top: 4%;
  margin-left: 7.5%;
}

.sub-title h3 {
  color:    #B9B9B9;
  font-size: 13px;
  font-weight: lighter;
}

.splitter {
  display: flex;
  align-self: center;
  width: 85%;
  min-height: 0.5px;
  background-color: grey;
  margin-top: 0px;
  margin-bottom: 4%;
}

.button {
  position: relative;
  margin-left: 7.5%;
  margin-bottom: 5%;
}

.button-container {
  margin-left: 30px;
}

.button form i {
  color: white;
  font-size: 14px;
  transition: 0.3s;
  position: absolute;
  left: 0px;
  top: 0px;
  padding: 5px 0px;
}

.button input:hover+i {
  color: dodgerblue;
}

Answer 1

now check it out only i added overflow: auto to your .side-bar container

*:focus {
  outline: none;
}

body {
  background-color: #F1F1FA;
  font-family: sans-serif;
  margin: 0;
  padding: 0;
}

.wrapper {
  height: 100vh;
}

.top-bar {
  display: flex;
  position: absolute;

  left: 17%;
  width: 83%;
  height: 50px;
  background-color: white;
  box-shadow: 0 2px 4px 0 rgba(0,0,0,0.10);
}

.search-input {
  align-self: center;
  margin-left: 10px;
}

.search-input form input[type="text"] {
  padding: 5px;
}

input[type="button"] {
  border: none;
  background-color: Transparent;
  outline: none;
  height: 20px;
  width: 92%;
  font-size: 13px;
  font-weight: regular;
  color: #B9B9B9;
  text-align: left;
}

.side-bar {
  display: flex;
  flex-direction: column;

  width: 17%;
  height: 100%;
  background-color: #272C32;
overflow: auto
}

.sub-title {
  margin-top: 4%;
  margin-left: 7.5%;
}

.sub-title h3 {
  color:    #B9B9B9;
  font-size: 13px;
  font-weight: lighter;
}

.splitter {
  display: flex;
  align-self: center;
  width: 85%;
  min-height: 0.5px;
  background-color: grey;
  margin-top: 0px;
  margin-bottom: 4%;
}

.button {
  position: relative;
  margin-left: 7.5%;
  margin-bottom: 5%;
}

.button-container {
  margin-left: 30px;
}

.button form i {
  color: white;
  font-size: 14px;
  transition: 0.3s;
  position: absolute;
  left: 0px;
  top: 0px;
  padding: 5px 0px;
}

.button input:hover+i {
  color: dodgerblue;
}

<div class="wrapper">
      <div class="top-bar">
        <div class="search-input">
          <form>
            <div class="input-field">
              <input type="text" placeholder="Search user" name="userPost">
            </div>
          </form>
        </div>
      </div>
      <div class="side-bar">
        <div class="sub-title">
          <h3>ADMIN TOOLS<h3>
        </div>
        <div class="splitter"></div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="Dashboard" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-tachometer-alt fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="Ban Panel" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-ban fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="Warn Panel" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-exclamation-circle fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="Gift Panel" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-gift fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="User Info" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-user fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
        <div class="sub-title">
          <h3>NEWS TOOLS<h3>
        </div>
        <div class="splitter"></div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="New Post" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-file fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="Remove Post" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-trash fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
        <div class="sub-title">
          <h3>OTHER<h3>
        </div>
        <div class="splitter"></div>
        <div class="button">
          <div class="button-container">
            <form>
              <input type="button" value="Game Statistics" onclick="window.location.href='http://www.google.com'"/>
              <i class="fas fa-chart-line fa-lg" aria-hidden="true"></i>
            </form>
          </div>
        </div>
      </div>
    </div>

Answer 2

Use 100vh if you want the height of the window.

Also close your <h3> tags with </h3>