<div class="app-layout">
  <div class="teams box">Teams</div>
  <div class="channels box">Channels</div>
  <div class="header box">Header</div>
  <div class="messages box">
    <ul class="message-list">
      <li></li>
      <li></li>
      <li></li>
      <li></li>
      <li></li>
      <li></li>
      <li></li>
      <li></li>
      <li></li>
      <li></li>
      <li></li>
      <li></li>
    </ul>
  </div>
  <div class="input box">
    <input type="text" placeholder="Have you tried the CSS Grid Layout Module?">
  </div>
</div>

*,
*:before,
*:after {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: Arial;
  background-color: #f2f2f2;
}

.box {
  color: #fff;
  padding: 1em;
  text-align: center;
}

input {
  width: 100%;
  padding: 1em;
  outline: none;
  border: 1px solid #f2f2f2;
}

.message-list {
  margin: 0;
  padding: 0;
}

.message-list li {
  padding: .2em;
  margin-top: 1em;
  margin-bottom: 1em;
  background-color: #f2f2f2;
}

.header {
  background-color: #ffffff;
}

.teams {
  background-color: #362233;
}

.channels {
  background-color: #52364E;
}

.messages {
  background-color: #ffffff;
}

.write {
  background-color: #f2f2f2;
}


/* Grid Layout Code */

.app-layout {
  display: grid;
  height: 100vh;
  grid-template-columns: 100px 250px 1fr;
  grid-template-rows: auto 1fr auto;
  grid-template-areas: "teams channels header" "teams channels messages" "teams channels input";
}

.teams {
  grid-area: teams;
}

.channels {
  grid-area: channels;
}

.header {
  grid-area: header;
  color: #333;
  border-bottom: 1px solid #f2f2f2;
}

.messages {
  grid-area: messages;
  padding: 0 1em;
  overflow-y: scroll;
}

.input {
  grid-area: input;
}