* {
  box-sizing: border-box;
}

body {
  font-family: "Arial", sans-serif;
  background-color: whitesmoke;
  margin: 0;
  padding: 0;
}

.container {
  max-width: 600px;
  margin: 50px auto;
  padding: 20px;
  background-color: white;
  border-radius: 10px;
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.5);
  text-align: center;
  transition: 3s;
}

h1 {
  color: #333;
}

input {
  padding: 10px;
  font-size: 16px;
  margin: 10px 0;
  width: 80%;
  border-radius: 5px;
  border: 1px solid #ddd;
  transition: 0.2s;
}

button {
  padding: 10px 20px;
  font-size: 16px;
  cursor: pointer;
  border-radius: 5px;
  border: none;
  background-color: #4caf50;
  color: white;
}

button:hover {
  background-color: #35a041;
}

#result {
  margin-top: 20px;
  font-size: 25px;
}

.correct {
  color: green;
}

.incorrect {
  color: red;
}

#navigation {
  position: fixed; /* fix to viewport */
  bottom: 0; /* place at bottom of viewport */
  left: 50%;
  transform: translate(-50%, 0);
  max-width: 480px; /* mimic largest phone width */
  width: 100vw; /* width of viewport */
  height: 4.5em;
  text-align: center;
  background-color: #ffffff;
  border-radius: 10px;
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.5);
  z-index: 200;
}

/* nav menu options */
nav > a {
  display: inline-block;
  /* for max-width and width, divide by number of screens */
  max-width: calc((480px / 4) - 4px);
  width: calc((100vw / 4) - 4px);
  margin: 0;
  padding: 0.5em 0;
  text-align: center;
  background-color: #ffffff;
  color: #888888;
  transition: 0.2s;
}

/* hover effect for nav menu options */
nav > a:hover {
  background-color: #eeeeee;
  cursor: pointer;
}

/* .active class indicates current screen within nav menu */
nav > a.active {
  background-color: #ffffff;
  color: #0099ff;
}

/* nav menu icon label */
nav > a > p {
  font-size: 0.75em;
  margin: 0.5em 0 0;
}

.letter-table {
  width: 100%;
  border-collapse: collapse;
  margin-top: 20px;
  transition: 0.2s;
}

.letter-table td {
  width: 40px;
  height: 40px;
  text-align: center;
  font-size: 24px;
  cursor: pointer;
  border: 1px solid #ddd;
  box-shadow: 0 4px 8px rgba(0, 0, 0, 0.5);
  transition: 0.1s;
}

.letter-table td:hover {
  scale: 1.3;
  background-color: lightblue;
}

dialog {
  text-align: center;
}

.number-display {
  font-size: 75px;
  font-weight: bold;
}

@supports (-webkit-appearance: none) or (-moz-appearance: none) {
  .checkbox-wrapper-13 input[type=checkbox] {
    --active: #275EFE;
    --active-inner: #fff;
    --focus: 2px rgba(39, 94, 254, .3);
    --border: #BBC1E1;
    --border-hover: #275EFE;
    --background: #fff;
    --disabled: #F6F8FF;
    --disabled-inner: #E1E6F9;
    -webkit-appearance: none;
    -moz-appearance: none;
    height: 21px;
    outline: none;
    display: inline-block;
    vertical-align: top;
    position: relative;
    margin: 0;
    cursor: pointer;
    border: 1px solid var(--bc, var(--border));
    background: var(--b, var(--background));
    transition: background 0.3s, border-color 0.3s, box-shadow 0.2s;
  }
  .checkbox-wrapper-13 input[type=checkbox]:after {
    content: "";
    display: block;
    left: 0;
    top: 0;
    position: absolute;
    transition: transform var(--d-t, 0.3s) var(--d-t-e, ease), opacity var(--d-o, 0.2s);
  }
  .checkbox-wrapper-13 input[type=checkbox]:checked {
    --b: var(--active);
    --bc: var(--active);
    --d-o: .3s;
    --d-t: .6s;
    --d-t-e: cubic-bezier(.2, .85, .32, 1.2);
  }
  .checkbox-wrapper-13 input[type=checkbox]:disabled {
    --b: var(--disabled);
    cursor: not-allowed;
    opacity: 0.9;
  }
  .checkbox-wrapper-13 input[type=checkbox]:disabled:checked {
    --b: var(--disabled-inner);
    --bc: var(--border);
  }
  .checkbox-wrapper-13 input[type=checkbox]:disabled + label {
    cursor: not-allowed;
  }
  .checkbox-wrapper-13 input[type=checkbox]:hover:not(:checked):not(:disabled) {
    --bc: var(--border-hover);
  }
  .checkbox-wrapper-13 input[type=checkbox]:focus {
    box-shadow: 0 0 0 var(--focus);
  }
  .checkbox-wrapper-13 input[type=checkbox]:not(.switch) {
    width: 21px;
  }
  .checkbox-wrapper-13 input[type=checkbox]:not(.switch):after {
    opacity: var(--o, 0);
  }
  .checkbox-wrapper-13 input[type=checkbox]:not(.switch):checked {
    --o: 1;
  }
  .checkbox-wrapper-13 input[type=checkbox] + label {
    display: inline-block;
    vertical-align: middle;
    cursor: pointer;
    margin-left: 4px;
  }

  .checkbox-wrapper-13 input[type=checkbox]:not(.switch) {
    border-radius: 7px;
  }
  .checkbox-wrapper-13 input[type=checkbox]:not(.switch):after {
    width: 5px;
    height: 9px;
    border: 2px solid var(--active-inner);
    border-top: 0;
    border-left: 0;
    left: 7px;
    top: 4px;
    transform: rotate(var(--r, 20deg));
  }
  .checkbox-wrapper-13 input[type=checkbox]:not(.switch):checked {
    --r: 43deg;
  }
}

.checkbox-wrapper-13 * {
  box-sizing: inherit;
}
.checkbox-wrapper-13 *:before,
.checkbox-wrapper-13 *:after {
  box-sizing: inherit;
  }