style.css

* {
  box-sizing: border-box;
}

html {
  font-family: Arial, Helvetica, sans-serif;
  font-size: 16px;
}

body {
  background-color: #e5e5e5;
  margin: 0;
}

.container {
  max-width: 1600px;
  margin: 0 auto;
  padding-left: 2rem;
  padding-right: 2rem;
}

header {
  background-color: #e5e5e5;
  border-bottom: 2px solid #ccc;
  padding-top: 1rem;
  position: sticky;
  top: 0;
  z-index: 100;
}

.calendar-header {
  display: flex;
  margin-left: 4rem;

  & > * {
    flex: 1;
  }
}

.day-head {
  font-weight: bold;
  font-size: 1.2rem;
  color: #555;
  padding: 0.5rem;
}

.calendar-body {
  position: relative;
}

.calendar-main {
  display: grid;
  grid-template-columns: 4rem 1fr;
  margin-bottom: 4rem;
}

.grid {
  display: grid;
  grid-template-columns: repeat(7, 1fr);
  position: relative;
}

.timeline-cell {
  height: 60px;
  text-align: right;
  color: #555;
  padding: 0.25rem 0.5rem;
}

.cell {
  height: 60px;
  border: 1px solid #ccc;
}

.items-view {
  position: absolute;
  top: 0;
  left: 0;
  right: 0;
  bottom: 0;
  display: flex;
}

.day-column {
  flex: 1;
  display: grid;
  grid-template-columns: 1fr;
  align-items: start;
  
  & > * {
    grid-area: 1 / 1 / 1 / 1;
  }
}

.calendar-item {
  background-color: white;
  border-radius: 5px;
  padding: 0.5rem;
  margin-right: 5px;
  box-shadow: 0 0 0.25rem rgba(0, 0, 0, 0.1);
}

.item-event {
  background-color: #52B2C0;
}

.item-task {
  background-color: white;
}

.task-done {
  text-decoration: line-through;
}