styles.css

:root {
  --toolbox-width: 320px;
}

body {
  padding: 0;
  margin: 0;
}

.container {
  display: flex;
  width: 100%;
  height: 100%;
  position: relative;
  overflow: hidden;
}

.display {
  width: calc(100% - var(--toolbox-width));
  height: 100%;
  display: flex;
  justify-content: center;
  align-items: center;
  user-select: none;
  background-color: black;
  color: white;
  cursor: move;
}

.toolbox {
  width: var(--toolbox-width);
  box-sizing: border-box;
  background-color: black;
  color: white;
  border-left: 1px dashed white;
}

.toolbox .scrollable {
  display: grid;
  height: 100%;
  box-sizing: border-box;
  overflow-y: auto;
  grid-template-columns: min-content 1fr;
  grid-auto-rows: min-content;
  column-gap: 25px;
  row-gap: 10px;
  padding: 10px 20px;
}

.toolbox label {
  white-space: nowrap;
}

.toolbox .toolbox-toggle {
  display: none;
}

#animate,
#lockcursor,
#copy,
#reset {
  grid-column: span 2;
}

@media screen and (max-width: 900px) {
  .display {
    width: 100%;
  }

  .toolbox {
    position: absolute;
    top: 0;
    right: 0;
    height: 100%;
    width: auto;
    transform: translateX(100%);
    transition: .2s all ease-in;
  }

  .toolbox .scrollable {
    grid-template-columns: 1fr;
    row-gap: 10px;
    padding: 10px 7px;
  }

  .toolbox .toolbox-toggle {
    display: block;
    position: absolute;
    top: 15px;
    left: 0;
    transform: translateX(calc(-100% - 15px));
  }

  .toolbox.opened {
    transform: translateX(0);
  }

  #animate,
  #lockcursor,
  #copy,
  #reset {
    grid-column: span 1;
  }
}