app.css

* {
  font-family: Fira Sans;
  background-color: #eeeeee;
}

main {
  margin: auto;
  max-width: 75%;
}

#flex_container {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  align-items: center;
}

h1 {
  font-size: 25pt;
}

td {
  text-align: center;
}

/* images */
img {
  max-width: 40%;
  height: auto;
}

#img_bg6 {
  border: 2px solid #eb1c24;
  border-radius: 12px;
}

#img_io {
  border: 2px solid #6b80e9;
  border-radius: 12px;
}

figcaption {
  font-size: 16pt;
  margin: 12px 6px;
  padding: 16px 32px;
  border: 2px dotted #000000;
  border-radius: 12px;
  display: flexbox;
  background-color: #fefee3;
}

#red {
  color: red;
  background-color: #fefee3;
}

#blue {
  color: blue;
  background-color: #fefee3;
}

p {
  font-size: 14pt;
}

/* buttons */
input {
  padding: 16px 32px;
  text-decoration: none;
  display: inline-block;
  font-size: 16pt;
  margin: 4px 2px;
  transition-duration: 0.4s;
  cursor: pointer;
}

#button_bg6 {
  background-color: #eb1c24;
  color: white;
  border: 2px solid #eb1c24;
  border-radius: 12px;
}

#button_bg6:hover {
  background-color: white;
  color: #eb1c24;
}

#button_io {
  background-color: #6b80e9;
  color: white;
  border: 2px solid #6b80e9;
  border-radius: 12px;
}

#button_io:hover {
  background-color: white;
  color: #6b80e9;
}

#button_rev {
  background-color: #555555;
  color: white;
  border: 2px solid #555555;
  border-radius: 12px;
}

#button_rev:hover {
  background-color: white;
  color: #555555;
}

#button_reset {
  background-color: black;
  color: white;
  border: 2px solid black;
  border-radius: 12px;
}

#button_reset:hover {
  background-color: white;
  color: black;
}

/* counter */
.counter {
  font-size: 40pt;
}