style.css

/*==============================
  GENERAL STYLES
================================*/

/*https://css-tricks.com/inheriting-box-sizing-probably-slightly-better-best-practice/*/
*, html {
  box-sizing: border-box;
  margin:0;
  padding:0;
}

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

body {
  font: 1.5em Helvetica, Arial;
  height: 100%;
  padding-bottom: 2.3em;
  overflow:auto;
}



/*==============================
  #MESSAGE-INPUT-FORM
================================*/
form {
  background: #2c3e50;
  height: 2.3em;
  width: 100%;
  display: flex;
  padding: 3px;
  position: fixed;
  bottom: 0;
  margin: 0;
}

  form input {
    border: 0;
    font-size: 1em;
    /*height: 2px;*/
    height: 2em;
    min-width: 70%;
    flex: 1;
    padding:0.5em;
    margin-right: .5%;
  }

  form button {
    background: #27ae60;
    border: none;
    color: white;
    font-size: 1em;
    height: 2em;
    padding: 10px;
  }

/*==============================
  #JOINING-CHAT-STRAPLINE
================================*/

#joiners {
  background-color:#2c3e50;
  color: white;
  opacity:0.9;
  z-index: 3;
  font-size: 1em;
  text-align: center;
  padding: 0.5em;
  word-wrap: break-word;
}

#joined  { color: #40d47e; }



/*==============================
  #MESSAGES-WINDOW
================================*/
#messages {
  list-style-type: none;
  margin: 0;
  max-height: 90%;
  padding: 0;
}

  #messages li { padding: 5px 10px; }

    #messages li:nth-child(odd) { background: #eee; }


/* == Individual messages == */
.time { color: #9c9c9c; }

.name {
  color: #2980b9;
  margin-right: 0.8em;
  word-wrap: break-word;
}

.name,
.time {
  font-size: 0.7em;
}

/*==============================
  MEDIA QUERIES
================================*/

@media only screen and (min-width: 768px) {

  .name {
    font-size: 1em;
  }

  .name,
  .time {
    font-size: .8em;
  }

  #joiners {
    height: 2em;
    font-size: 1.5em;
    padding: 0.5em 0 1em 2em;
    text-align: left;
  }
}