style.css

body {
  margin: 0;
  padding: 0;
  background-color: #e4e4e4;
}

hr {
  border-color: #d1d1d1;
}

.toolbox {
  position: absolute;
  height: 100vh;
  background-color: #454647;
}

.toolbox.left {
  left: 0;
  top: 0;
}

.toolbox.right {
  right: 0;
  top: 0;
  overflow-y: auto;
}

.toolbox .group .item {
  width: 24px;
  height: 24px;
  padding: 10px;
  cursor: pointer;
}

.toolbox .group .item:hover,
.toolbox .group .item.active {
  background-color: #007aff;
}

.toolbox .group .item img {
  width: 100%;
  filter: invert();
}

.toolbox .group.linewidths .item {
  position: relative;
}

.toolbox .group.linewidths .item .linewidth {
  position: absolute;
  background-color: #ffffff;
  border-radius: 50%;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

.toolbox .group.swatches .item .swatch {
  width: 100%;
  height: 100%;
  border: 1px solid #d1d1d1;
  box-sizing: border-box;
}

.header {
  margin: 50px 100px;
}

.custom-file-input {
  overflow: hidden;
  position: relative;
}

.custom-file-input [type="file"] {
  cursor: inherit;
  display: block;
  font-size: 999px;
  filter: alpha(opacity=0);
  min-height: 100%;
  min-width: 100%;
  opacity: 0;
  position: absolute;
  right: 0;
  text-align: right;
  top: 0;
}

canvas {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%);
  background-color: #ffffff;
}

.no-mobile {
  display: none;
}

@media (max-width: 576px) {
  .toolbox,
  canvas {
    display: none;
  }
  .no-mobile {
    display: flex;
    align-items: center;
    height: 100vh;
    padding: 0 1rem;
    color: #98a6ad;
    text-align: center;
  }
}