:root {
  --hover-color: orange; /* global scope */
  --pressed-color: green;
}

h1 {
    margin: 0px;
}

#header {
    display: flex;
    flex-direction: row;
    align-content: center;
    align-items: center;
    justify-content: space-around;
    font-family: monospace;
    height: 4rem;
}

body {
    background-color: black;
    color: white;
    margin: 0px;
}

button {
    background-color: black;
    color: white;
    border: 1px solid white;
    margin: 0px;
    padding: 5px;
}

button:hover {border-color: var(--hover-color);}
button:active {border-color: var(--pressed-color);}


input,
button {
    box-sizing: border-box;
    height: 100%;
}

/* Chrome, Safari, Edge, Opera */
input::-webkit-outer-spin-button,
input::-webkit-inner-spin-button {
  -webkit-appearance: none;
  margin: 0;
}