style.css

body{
  background: #f6f6f6;
  font-family: 'Roboto', sans-serif;
}

.game-container {
  width: 100vw;
  height: 100vh;
  margin: 0;
  display: table-cell;
  text-align: center;
  vertical-align: middle;
  font-size: 40px;
  color: #464646;
}

.start-menu {
  max-width: 300px;
  margin: 5vh auto;
  box-shadow: 0px 0px 3px gray;
  border-radius: 5px;
  padding: 20px;
  text-align: center;
  font-size: 16px;
}

.start-menu input, .start-menu select {
  background: 
  transparent;
  box-shadow: 0px 0px 1px;
  height: 30px;
  width: 100%;
}

.start-button {
  display: inline-block;
  box-shadow: 0px 0px 3px gray;
  background: #019501;
  color: #eee;
  padding: 8px;
  border-radius: 4px;
  cursor: pointer;
}

.exercise, .reply, .exercise-container {
  display: inline-block;
}

.reply {
  min-width: 50px;
  min-height: 50px;
  border: 1px dotted #464646;
  margin-left: 10px;
}

.reply::before {
  content: ' ';
}

.greenflash {
  animation-duration: 1s;
  animation-name: greenflash;
}

.redflash {
  animation-duration: 1s;
  animation-name: redflash;
}

.progress-bar{
  margin: 10px auto;
  max-width: 300px;
  text-align: center;
}

.load-bar{
  height: 10px;
  border-radius: 5px;
  /*margin: 0 auto;*/
  animation-duration: 10s;
  animation-name: filload;
}

.stats {
  position: absolute;
  top: 2vw;
  right: 2vw;
  font-size: 20px;
  text-align: right;
}

.footer {
  position: absolute;
  bottom: 10px;
  right: 10px;
  font-size: small;
}

@keyframes greenflash {
  from {
    background: green;
    color: white;
  }

  to {
    background: transparent;
    color: #464646;
  }
}

@keyframes redflash {
  from {
    background: red;
    color: white;
  }

  to {
    background: transparent;
    color: #464646;
  }
}

@keyframes filload {
  from {
    background: green;
    width: 100%;
  }
  
  to {
    background: red;
    width: 0%
  }
}