:root {
  --bg-color: #1E3A8A;
  --btn-bg-color: #2563EB;
  --text-btn: #93C5FD;
}

html {
  /* border: 5px solid blue; */
  padding: 0;
  margin: 0;
}

body {
  font-family: sans-serif;
  text-align: center;
  /* border: 2px solid green; */
  margin: 5em auto;
  background-color: var(--bg-color);
  color: var(--text-btn);
}
div {
  display: flex;
  flex-direction: column;
  justify-content: center;
  max-width: 900px;
  margin: auto;
}

p,
#result {
  font-size: 1.2rem;
}
input,
#result-btn {
  text-align: center;
  display: block;
  margin: 1em auto;
  padding: 1em;
  max-width: 600px;
  min-width: 250px;
  color: var(--text-btn);
  background-color: var(--bg-color);
  border: whitesmoke 2px solid;
  border-radius: 10px;
}
#result-btn {
  margin-top: 2em;
  width: 290px;
  color: var(--text-btn);
  background-color: var(--btn-bg-color);
}