style.css

html {
  --accent-first: rgb(137, 121, 211);
  --accent-first-transparent: rgba(137, 121, 211, 0.25);
  --accent-first-transparent-low: rgba(137, 121, 211, 0.5);
  --accent-second: rgb(72, 137, 221);
  --accent-third: rgb(25, 165, 207);
  --accent-fourth: rgb(12, 199, 209);
  --accent-fifth: rgb(206, 98, 218);
  --accent-gradient: linear-gradient(
    15deg,
    var(--accent-first) 25%,
    var(--accent-second) 50%,
    var(--accent-third) 75%,
    var(--accent-fourth) 100%
  );
  --colorful-gradient: linear-gradient(300deg, #8a2387, #e94057, #f27121);
  --orange-gradient: linear-gradient(
    150deg,
    rgb(245, 175, 25) 30%,
    rgb(241, 39, 17) 100%
  );
  --green-gradient: linear-gradient(20deg, #67b26f, #4ca2cd);
  --calm-gradient: linear-gradient(20deg, #5f2c82, #49a09d);
  --blue-gradient: linear-gradient(to right, #4facfe 0%, #00bdc7 100%);
  --purple-gradient: linear-gradient(135deg, #667eea 0%, #764ba2 100%);
  --greener-gradient: linear-gradient(to right, #11998e, #38ef7d);
  --cosmic-gradient: linear-gradient(330deg, #ff00cc, #333399);
  --playful-gradient: linear-gradient(340deg, #fc00ff, #27bcbe);
  --atlas-gradient: linear-gradient(300deg, #feac5e, #c779d0, #4bc0c8);
  --accent-contrast: rgb(255, 255, 255);
  --border-radius: 10px;
  --font-family: 'Helvetica Neue', 'Lucida Grande', 'Arial', 'Verdana', 'Tahoma',
    sans-serif;
}

html.light {
  --shadow-dark: 0 6px 10px rgba(40, 40, 40, 0.25);
  --shadow-darker: 0 6px 10px rgba(40, 40, 40, 0.4);
  --shadow-smooth: 0 1px 1px rgba(0, 0, 0, 0.08), 0 2px 2px rgba(0, 0, 0, 0.05),
    0 4px 4px rgba(0, 0, 0, 0.06), 0 8px 8px rgba(0, 0, 0, 0.1);
  --shadow-accent: 0 0 12px rgba(0, 150, 255, 0.9);
  --main-first: rgb(255, 255, 255);
  --main-first-transparent: rgba(255, 255, 255, 0.7);
  --main-second: rgb(245, 245, 245);
  --main-third: rgb(235, 235, 235);
  --main-third-transparent: rgba(235, 235, 235, 0.9);
  --main-fourth: rgb(225, 225, 225);
  --main-fifth: rgb(215, 215, 215);
  --main-contrast: rgb(50, 50, 50);
  --main-contrast-light: rgb(100, 100, 100);
  --main-contrast-lightest: rgb(150, 150, 150);
}

html.dark {
  --shadow-dark: 0 6px 10px rgba(40, 40, 40, 0.25);
  --shadow-darker: 0 6px 10px rgba(40, 40, 40, 0.4);
  --shadow-smooth: 0 1px 1px rgba(0, 0, 0, 0.08), 0 2px 2px rgba(0, 0, 0, 0.05),
    0 4px 4px rgba(0, 0, 0, 0.06), 0 8px 8px rgba(0, 0, 0, 0.1);
  --shadow-accent: 0 0 12px rgba(0, 150, 255, 0.9);
  --main-first: rgb(10, 10, 10);
  --main-first-transparent: rgba(10, 10, 10, 0.7);
  --main-second: rgb(25, 25, 25);
  --main-third: rgb(40, 40, 40);
  --main-third-transparent: rgba(40, 40, 40, 0.9);
  --main-fourth: rgb(50, 50, 50);
  --main-fifth: rgb(65, 65, 65);
  --main-contrast: rgb(255, 255, 255);
  --main-contrast-light: rgb(230, 230, 230);
  --main-contrast-lightest: rgb(200, 200, 200);
}

html {
  font-family: var(--font-family);
}
body {
  background: var(--main-third);
  color: var(--main-contrast);
  margin: 0;
  padding: 20px;
}
input,
button {
  outline: none;
  border: none;
}
div,
span,
input,
button,
textarea {
  transition: background 0.25s, color 0.25s, border-radius 0.25s;
}
a {
  text-decoration: none;
}
.noselect {
  -webkit-user-select: none;
  -khtml-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
  outline: none;
}
.hidden {
  display: none;
  visibility: hidden;
  position: absolute;
  z-index: -1;
}

button {
  background: var(--accent-first);
  padding: 10px;
  border-radius: var(--border-radius);
  color: var(--accent-contrast);
  cursor: pointer;
}
button:hover {
  background: var(--accent-second);
}

input[type='text'] {
  padding: 10px;
  border-radius: var(--border-radius);
  margin-top: 10px;
}

input {
  background: var(--main-first);
  color: var(--main-contrast);
}
input::placeholder {
  color: var(--main-contrast-lightest);
}

.checkbox-container {
  position: relative;
  display: flex;
  justify-content: flex-start;
  align-items: center;
  height: 25px;
  margin: 10px 0 10px 0;
  width: 240px;
}

.checkbox-container input {
  position: absolute;
  opacity: 0;
  cursor: pointer;
  height: 0;
  width: 0;
}

.checkbox-container label {
  margin: 0 20px 0 40px;
}

.checkbox-container .checkbox {
  position: absolute;
  top: 0;
  left: 0;
  height: 25px;
  width: 25px;
  margin-right: 20px;
  border-radius: 6px;
  cursor: pointer;
  background-color: var(--main-first);
}

.checkbox-container:hover input ~ .checkbox {
  background-color: var(--main-second);
}

.checkbox-container input:checked ~ .checkbox {
  background-color: var(--accent-first);
}

.checkbox-container .checkbox:after {
  content: '';
  position: absolute;
  display: none;
}

.checkbox-container input:checked ~ .checkbox:after {
  display: block;
}

.checkbox-container .checkbox:after {
  left: 9px;
  top: 5px;
  width: 5px;
  height: 10px;
  border: solid var(--accent-contrast);
  border-width: 0 3px 3px 0;
  -webkit-transform: rotate(45deg);
  -ms-transform: rotate(45deg);
  transform: rotate(45deg);
}

.buttons {
  margin-bottom: 20px;
}
button.active {
  background: rgb(109, 48, 126);
  color: var(--accent-contrast);
}

.settings {
  display: flex;
  max-width: 750px;
  flex-wrap: wrap;
  margin-bottom: 10px;
}
.settings div {
  width: 250px;
}

.key-container {
  display: flex;
}
.key-container input[type='text'] {
  padding: 5px 10px;
  height: 25px;
  margin-right: 20px;
}
.key-container .checkbox-container {
  width: 100px;
  margin-top: 15px;
}

#output {
  display: flex;
  width: 100%;
  max-width: 100%;
  justify-content: center;
  flex-direction: row;
  column-gap: 4px;
  margin-top: 20px;
  overflow: auto hidden;
}
@media screen and (max-width: 1520px) {
  #output {
    justify-content: flex-start;
  }
}
.column:first-of-type {
  background: var(--main-contrast);
}
.column:nth-of-type(13) {
  background: var(--main-contrast);
}
.column {
  display: flex;
  flex-direction: column;
  row-gap: 10px;
  padding: 6px;
  background: var(--main-fifth);
  border-radius: var(--border-radius);
}
.column .header {
  background: var(--main-first);
  cursor: default;
}
.column .header:hover {
  transform: none;
}
.column .header.active-key {
  background: var(--accent-fourth);
}
.column div {
  padding: 8px;
  border-radius: var(--border-radius);
  display: flex;
  justify-content: center;
  align-items: center;
  cursor: pointer;
  transition: transform 0.25s;
}
.column div:hover {
  transform: scale(0.9);
}

#output.note-color .column div[data-note='A'] {
  background: red;
  color: white;
}
#output.note-color .column div[data-note='A#'] {
  background: darkred;
  color: white;
}
#output.note-color .column div[data-note='B'] {
  background: cyan;
}
#output.note-color .column div[data-note='C'] {
  background: blue;
  color: white;
}
#output.note-color .column div[data-note='C#'] {
  background: darkblue;
  color: white;
}
#output.note-color .column div[data-note='D'] {
  background: orange;
  color: white;
}
#output.note-color .column div[data-note='D#'] {
  background: darkorange;
  color: white;
}
#output.note-color .column div[data-note='E'] {
  background: lightcoral;
}
#output.note-color .column div[data-note='F'] {
  background: green;
  color: white;
}
#output.note-color .column div[data-note='F#'] {
  background: darkgreen;
  color: white;
}
#output.note-color .column div[data-note='G'] {
  background: khaki;
}
#output.note-color .column div[data-note='G#'] {
  background: darkkhaki;
  color: white;
}

.n2 {
  background: rgb(240, 160, 40);
}
.n3 {
  background: rgb(70, 170, 225);
}
.n4 {
  background: rgb(160, 200, 60);
}
.n5 {
  background: rgb(220, 150, 190);
}
.n6 {
  background: rgb(240, 230, 80);
}

.column div.active {
  color: var(--accent-contrast);
}
.column:nth-of-type(even) div.active {
  background: rgb(190, 25, 25);
}
.column:nth-of-type(odd) div.active {
  background: rgb(150, 69, 69);
}

.column div.disabled {
  background: var(--main-second) !important;
  color: var(--main-contrast) !important;
}

.current-wrapper {
  margin: 40px auto;
  display: flex;
  width: 100%;
  justify-content: center;
  position: relative;
}
.current-wrapper #clear {
  height: 44px;
  padding: 0 10px;
  align-self: center;
  position: absolute;
  left: 0;
  width: 100px;
}
.current-wrapper #play {
  height: 44px;
  padding: 0 10px;
  align-self: center;
  position: absolute;
  width: 100px;
  left: 120px;
}
.current-wrapper #speed {
  height: 44px;
  padding: 0 10px;
  align-self: center;
  position: absolute;
  width: 100px;
  left: 240px;
  margin: 0;
}
.current-wrapper #save-settings {
  height: 44px;
  padding: 0 10px;
  align-self: center;
  position: absolute;
  width: 120px;
  right: 0;
}
.current-wrapper span {
  background: var(--main-fifth);
  padding: 10px;
  margin: 4px;
  line-height: 24px;
  border-radius: var(--border-radius);
}

#tabs {
  font-size: 0;
}

#tabs .block {
  font-size: 14px;
  display: inline-block;
  margin-bottom: 20px;
  color: var(--main-contrast);
  cursor: pointer;
  transition: transform 0.5s, background 0.5s, opacity 0.5s;
  border-radius: 10px;
}
#tabs .block:hover {
  transform: scale(0.8);
  background: rgba(255, 0, 0, 0.5);
  opacity: 0.8;
}

#tabs .line-2,
#tabs .line-3,
#tabs .line-4 {
  height: 1px;
  background: var(--main-contrast);
  display: inline-block;
  vertical-align: middle;
}

#tabs .line-2 {
  width: 28px;
}

#tabs .line-3 {
  width: 100%;
}

#tabs .line-4 {
  width: 100%;
}