styles.css

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  font-family: sans-serif;
  line-height: 1.5;
}

/* Main */
.main {
  display: block;
  margin: 0 auto;
}

/* Mensajes */
.messages {
  padding: 1rem;
}

/* Control */
.control {
  position: fixed;
  left: 0;
  right: 0;
  bottom: 0;

  display: block;
  overflow: hidden;
  background-color: #fff;
  border-top: 6px solid #005eba;
}
.control input {
  display: block;
  float: left;
  margin: 0;
  border: 0;
  padding: 0.5rem;
  width: calc(100% - 6rem);
  height: 3rem;
  line-height: 2rem;
  font-size: 1rem;
}
.control button {
  display: block;
  float: left;
  margin: 0;
  border: 0;
  padding: 0.5rem 1rem;
  width: 6rem;
  height: 3rem;

  background: #005eba;
  line-height: 2rem;
  font-size: 1rem;
  color: #fff;
  cursor: pointer;
}
#username {
  border-right: 2px solid #005eba;
  width: 10rem;
  font-weight: bold;
}
#value {
  width: calc(100% - 16rem);
}