canvas.css

:root {
  --toolbar-height: 48px;
  --toolbar-background: #202020;
  --toolbar-background-selected: #1E538F;
  --toolbar-background-hover: #000000;
  --left-panel-background-selected: #87B9E7;
}

body {
  margin: 0;
  padding: 0;
  overflow: hidden;
}

#toolbar {
  height: var(--toolbar-height);
  background-color: var(--toolbar-background);
}

.toolbar-button {
  background-color: unset;
  border: none;
  color: white;
  height: 100%;
}
.toolbar-button-selected {
  background-color: var(--toolbar-background-selected);
}
.toolbar-button:hover {
  background-color: var(--toolbar-background-hover);
}

#editor {
  height: calc(100vh - var(--toolbar-height));
  display: flex;
}

#canvas {
  outline: none;
}

#left-panel {
  margin-block-start: unset;
  margin-block-end: unset;
  padding-inline-start: unset;
}

.left-panel-option {
  list-style: none;
}

.left-panel-option > button {
  background-color: unset;
  border: solid 1px transparent;
}

.left-panel-option > button:hover {
  box-sizing: border-box;
  border: solid 1px var(--left-panel-background-selected);
}

.left-panel-option-selected > button {
  background-color: var(--left-panel-background-selected);
}