style.css

* {
  box-sizing: border-box;
/*   margin: 0;
  padding: 0; */
}

body {
  display: flex;
  justify-content: center;
  align-items: center;
  flex-direction: column;
  background-color: #191919;
  min-height: 100vh;
}

input {
  border: none;
  color: inherit;
  font-size: inherit;
  font-weight: inherit;
  font-family: inherit;
}

h1 {
  font-family: 'Montserrat', sans-serif;
  font-size: 24px;
  color: #fff;
}

button {
  border-radius: 10px;
  cursor: pointer;
  height: 40px;
  width: 50px;
  border: none;
}
button:hover {
  background-color: darkgray;
}
button:active {
  background-color: green;
}

.teclado {
  display: grid;
  grid-template-columns: repeat(3, 1fr);
  gap: 10px; 
  background-color: #cccccc;
  border-radius: 30px;
  padding: 10px;
}

input[type=button] {
  border-radius: 20px;
  cursor: pointer;
  font-family: 'Montserrat', sans-serif;
  height: 80px;
  width: 80px;
}
input[type=button]:hover {
  background-color: darkgray;
}

input[type=button]:active {
  background-color: green;
}

.ajuste {
  display: flex;
}

input[type=tel] {
  background-color: #cccccc;
  border-radius: 10px;
  font-family: monospace;
  font-size: 15px;
  height: 40px;
  margin-bottom: 24px;
  padding: 10px;
  text-align: center;
  width: 210px;
  margin-right: 6px;
}

.ativa {
  background-color: red;
}

footer {
  background-color: white;
  margin-top: 130px;
  color: purple;
  text-align: center;
  width: 100%;
}