style.css

/* BASIC STLYING  */
html {
  box-sizing: border-box;
}

*,
*:before,
*:after {
  box-sizing: inherit;
  margin: 0;
  padding: 0;
}

body {
  font-family: 'Roboto', sans-serif;
  font-size: 1rem;
}

/* HEADER SECTION STLYE */
h1 {
  text-align: center;
  padding: 2rem;
}

/* TILE STLYING  */
.centre {
  display: flex;
  align-items: center;
  justify-content: center;
}

.tile-stlyes>* {
  display: flex;
  align-items: center;
  justify-content: center;

  margin: 0.5rem;
  width: 2.5rem;
  height: 2.5rem;
  text-transform: uppercase;
  border: 1px solid black;
  border-radius: 10px;
}

/*SIZES FOR DESKTOP LAYOUT*/
@media (min-width: 650px) {
  .tile-stlyes>* {
    width: 3.5rem;
    height: 3.5rem;
  }
}

/* KEYBOARD STLYING  */
.container_keyboard {
  display: flex;
  flex-direction: column;
  align-items: center;
  margin-top: 2rem;
}

.margin-top>*+* {
  margin-top: 0.7rem;
}

button {
  cursor: pointer;
  width: 1.7rem;
  height: 1.7rem;
}
/* ENTER & BACK KEYS  */
.row-three button:first-child,
.row-three button:last-child {
  width: 3.2rem;
}

/*SIZES FOR DESKTOP LAYOUT*/
@media (min-width: 650px) {
  button {
    width: 3rem;
    height: 3rem;
  }
/* ENTER & BACK KEYS  */
  .row-three button:first-child,
  .row-three button:last-child {
    width: 5rem;
  }
}