/* Global styles for a clean look */
body {
  font-family: 'Inter', sans-serif;
  background-color: #f0f2f5;
  color: #333;
  margin: 0;
  padding: 0;
}

/*
* Main container for the timeline.
* Uses a relative position to serve as the anchor for the absolute-positioned vertical line.
* The width is set to 90% and is centered for a clean layout on all screen sizes.
*/
.lessons-container {
  position: relative;
  margin: 0 auto;
  max-width: 90%;
  padding: 50px 0;
}

/*
* The vertical timeline line.
* It's a pseudo-element (`::before`) to create a single, elegant line down the center.
* Positioned absolutely to stay in place as you scroll.
*/
.lessons-container::before {
  content: '';
  position: absolute;
  top: 0;
  left: 50%;
  width: 4px;
  height: 100%;
  background-color: #e0e0e0;
  transform: translateX(-50%);
}

/*
* The base style for each individual lesson card.
* The cards are positioned to the left and right of the central line.
* 'opacity: 0' and 'transform' are the starting states for the animation.
*/
.lesson-card {
  position: relative;
  background-color: #fff;
  border-radius: 12px;
  box-shadow: 0 8px 24px rgba(0, 0, 0, 0.1);
  padding: 30px;
  margin-bottom: 80px;
  box-sizing: border-box;
  transition: opacity 0.6s ease-out, transform 0.6s ease-out;
  opacity: 0;
  width: calc(50% - 40px); /* Adjusting width for the new layout */
  z-index: 2; /* Ensures cards are above the timeline line */
}

/*
* Positioning for the left-side cards.
* The margin pushes them away from the center line.
*/
.lessons-container .lesson-card:nth-child(odd) {
  margin-right: calc(50% + 40px);
  transform: translateX(-20px);
}

/*
* Positioning for the right-side cards.
* The margin pushes them away from the center line.
*/
.lessons-container .lesson-card:nth-child(even) {
  margin-left: calc(50% + 40px);
  transform: translateX(20px);
}

/*
* The class added by JavaScript when a card enters the viewport.
* It makes the card visible and moves it into its final position.
*/
.lesson-card.show {
  opacity: 1;
  transform: translateX(0);
}

/*
* The class added by JavaScript to cards that have been scrolled past.
* It fades them out to create the "disappearing" effect.
*/
.lesson-card.hide {
  opacity: 0;
  transition: opacity 0.6s ease-out;
  transform: translateX(0);
}

/*
* The number marker's base style.
* Positioned absolutely to sit on the central timeline line.
*/
.lesson-number {
  position: absolute;
  left: 50%;
  top: 50%;
  transform: translate(-50%, -50%);
  color: #fff;
  font-weight: bold;
  font-size: 24px;
  border-radius: 50%;
  width: 50px;
  height: 50px;
  display: flex;
  align-items: center;
  justify-content: center;
  box-shadow: 0 4px 12px rgba(0, 0, 0, 0.15);
  z-index: 3; /* Ensures numbers are on top of everything */
}

/* Styles for the content inside the card */
.lesson-card-content {
  padding: 10px;
}

.lesson-title {
  font-size: 28px;
  font-weight: bold;
  margin-bottom: 10px;
}

.lesson-description {
  font-size: 16px;
  color: #333;
  line-height: 1.6;
  margin-bottom: 15px;
}

.supportive-quote {
  font-size: 14px;
  font-style: italic;
  color: #555;
  border-left: 3px solid #ddd;
  padding-left: 15px;
  margin: 15px 0;
}

.lesson-resource {
  display: inline-block;
  margin-top: 10px;
  font-weight: bold;
  color: #0077B6;
  text-decoration: none;
}

.lesson-footnote {
  font-size: 12px;
  color: #999;
  margin-top: 10px;
}

/*
* Unique color themes for each card.
* The `.card-theme-X` class is applied to the main card container.
*/
.card-theme-1 .lesson-number { background-color: #00B8A1; }
.card-theme-1 .lesson-title { color: #00B8A1; }

.card-theme-2 .lesson-number { background-color: #008C9E; }
.card-theme-2 .lesson-title { color: #008C9E; }

.card-theme-3 .lesson-number { background-color: #0077B6; }
.card-theme-3 .lesson-title { color: #0077B6; }

.card-theme-4 .lesson-number { background-color: #0096C7; }
.card-theme-4 .lesson-title { color: #0096C7; }

.card-theme-5 .lesson-number { background-color: #00B4D8; }
.card-theme-5 .lesson-title { color: #00B4D8; }

.card-theme-6 .lesson-number { background-color: #2196C1; }
.card-theme-6 .lesson-title { color: #2196C1; }

.card-theme-7 .lesson-number { background-color: #5BC0DE; }
.card-theme-7 .lesson-title { color: #5BC0DE; }

.card-theme-8 .lesson-number { background-color: #007F5F; }
.card-theme-8 .lesson-title { color: #007F5F; }

.card-theme-9 .lesson-number { background-color: #023E8A; }
.card-theme-9 .lesson-title { color: #023E8A; }

.card-theme-10 .lesson-number { background-color: #03045E; }
.card-theme-10 .lesson-title { color: #03045E; }

.card-theme-11 .lesson-number { background-color: #4F98CA; }
.card-theme-11 .lesson-title { color: #4F98CA; }

.card-theme-12 .lesson-number { background-color: #1CA9C9; }
.card-theme-12 .lesson-title { color: #1CA9C9; }

/* Media queries for smaller screens */
@media (max-width: 768px) {
  .lessons-container::before {
    left: 20px;
    transform: none;
  }
  .lesson-card {
    width: calc(100% - 40px); /* Full width for mobile */
    margin-left: 40px !important; /* Forces all cards to the right of the line */
    margin-right: 0 !important;
  }
  /* Resetting the transforms for mobile to a single direction */
  .lessons-container .lesson-card:nth-child(odd),
  .lessons-container .lesson-card:nth-child(even) {
    transform: translateX(0); /* All cards start at the same position */
  }
  /* Adjusting the scroll-in animation for mobile */
  .lesson-card.show {
    transform: translateX(0);
  }
  .lesson-card.hide {
    transform: translateX(-20px); /* Hide to the left */
  }
  .lesson-number {
    left: 20px;
    transform: translateX(-50%);
  }
}