style.css

/* General set up */

* {
  box-sizing: border-box;
}

html {
  font-family: sans-serif;
  margin: 0;
  /* Use overscroll-behavior to stop the "bounce" or refresh effect you get on mobile
  browsers when getting to the top or bottom scroll limits of the page */
  overscroll-behavior: none;
}

/* Styling of contacts */

header,
footer {
  background-color: #a60000;
  color: white;
  text-align: center;
  height: 50px;
  line-height: 50px;
  text-shadow: 2px 2px 1px black;
}

h1,
h2 {
  margin: 0;
}

main div {
  padding: 10px 20px;
  border-bottom: 1px solid #eee;
}

p {
  margin: 0;
}

a {
  color: #ccc;
}

main div p {
  line-height: 20px;
}

body > header {
  position: sticky;
  top: 0;
}

/* Styling of chatbox */

.chatbox {
  background: white;
  width: 200px;
  height: 300px;
  border: 1px solid black;
  position: fixed;
  bottom: 10px;
  right: 10px;
}

.messages {
  height: 220px;
  overflow: auto;
  /* use overscroll-behavior-y to stop page scrolling behind the chatbox,
  when the chatbox's scroll limits are reached */
  overscroll-behavior-y: contain;
}

.messages p {
  margin: 10px;
  padding: 10px;
  border-radius: 3px;
}

.me {
  background-color: #bbb;
}

.you {
  background-color: #eee;
  text-align: right;
}

.chatbox form {
  height: 30px;
  display: flex;
}

form input,
form button {
  display: block;
}

form input {
  width: 70%;
}

form button {
  width: 30%;
  font-size: 0.7rem;
}