index.css

body {
  margin: 0;
}

.hidden {
  display: none !important;
}

.root {
  height: 100vh;
  overflow: auto;
}

.toolbar {
  position: sticky;
  top: 0;
  left: 0;
  padding: 8px;
  background-image: linear-gradient(#fff, rgba(255, 255, 255, 0.4));
  z-index: 10;
}
.toolbar > * {
  vertical-align: middle;
}
.toolbar > .open {
  width: 160px;
}

table {
  border-spacing: 0;
  margin: 8px;
}

tr.header {
  position: sticky;
  top: 43px;
  z-index: 5;
}
td {
  border: 1px solid #ddd;
  min-width: 80px;
  height: 1em;
  line-height: 1;
  position: relative;
  outline: none;
}
td.header-left {
  position: sticky;
  left: 0;
  z-index: 5;
  background-color: #eee;
  min-width: 20px;
  text-align: center;
}
td.header-top {
  background-color: #eee;
  text-align: center;
}

td:focus,
td.selected {
  background-color: #dfd;
}

td.selected-top {
  border-top: 1px solid green;
}
td.selected-left {
  border-left: 1px solid green;
}
td.selected-right {
  border-right: 1px solid green;
}
td.selected-bottom {
  border-bottom: 1px solid green;
}

.color-picker {
  background-color: rgba(0,0,0,0.2);
  display: flex;
  align-items: center;
  justify-content: center;
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  z-index: 1000;
}
.color-picker .close {
  position: absolute;
  top: 20px;
  right: 20px;
  padding: 12px 20px;
  font-size: 20px;
}
.color-picker .colors-item {
  display: flex;
}
.color-picker .colors-item>div {
  width: 30px;
  height: 30px;
  margin: 4px;
  box-shadow: 0 0 8px #888;
}