body {
  margin: 0;
  padding: 0;
  font-family: 'Comic Sans MS', cursive, sans-serif;
  background: #f5f5f5;
  overflow: hidden;
}
.cover {
  /* cover-{三级知识点.png} */
  background-image: url('https://static0.xesimg.com/math-fe/khan-video/ela/cover-Grammar.png');
}
.learn {
  /* learn-{三级知识点.png} */
  background-image: url('https://static0.xesimg.com/math-fe/khan-video/ela/learn-Grammar.png');
}
.practice {
  /* practice-{三级知识点.png} */
  background-image: url('https://static0.xesimg.com/math-fe/khan-video/ela/practice-Grammar.png');
}
.slide-container {
  width: 1280px;
  height: 800px;
  margin: 0 auto;
  position: relative;
  background: #fff;
  overflow: hidden;
}
.slide-counter {
  position: fixed;
  bottom: 80px;
  left: 50%;
  transform: translateX(-50%);
  background: rgba(255, 255, 255, 0.9);
  padding: 8px 16px;
  border-radius: 20px;
  font-size: 16px;
  color: #333;
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.1);
  z-index: 1000;
}
.slide {
  width: 100%;
  height: 100%;
  position: absolute;
  top: 0;
  left: 0;
  display: none;
  padding: 80px 40px 0px;
  box-sizing: border-box;
  background-size: 100% 100%;
  background-repeat: no-repeat;
}
.slide.active {
  display: block;
}
.title {
  font-size: 50px;
  width: 727px;
  color: #2196f3;
  text-align: center;
  margin-top: 250px;
  margin-left: 207px;
  text-shadow: 2px 2px 4px rgba(0, 0, 0, 0.1);
  opacity: 0;
  transform: translateY(20px);
  transition: all 0.5s ease;
}
.subtitle {
  font-size: 36px;
  width: 727px;
  color: #666;
  text-align: center;
  margin-top: 60px;
  margin-left: 207px;
  opacity: 0;
  transform: translateY(20px);
  transition: all 0.5s ease;
}
.cover .text-item {
  padding-left: 6em;
}
.title.visible,
.subtitle.visible {
  opacity: 1;
  transform: translateY(0);
}
.story-text {
  font-size: 24px;
  line-height: 1.8;
  color: #333;
  padding: 20px;
  background: rgba(255, 255, 255, 0.9);
  border-radius: 15px;
  box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
  margin-top: 20px;
  opacity: 0;
  transform: translateY(20px);
  transition: all 0.5s ease;
  width: 100%;
  max-width: 800px;
}
.story-text.visible {
  opacity: 1;
  transform: translateY(0);
}
.story-text p {
  text-indent: 2em;
}
.content {
  font-size: 32px;
  color: #333;
  line-height: 1.6;
  padding: 40px;
  padding-top: 0px;
  max-width: 1000px;
  margin: 0 auto;
  display: flex;
  flex-direction: column;
  align-items: center;
}
.popup-container {
  position: absolute;
  top: 50%;
  left: 50%;
  transform: translate(-50%, -50%) scale(0);
  background: white;
  padding: 30px;
  border-radius: 15px;
  box-shadow: 0 0 30px rgba(0, 0, 0, 0.2);
  opacity: 0;
  transition: all 0.4s ease;
  max-width: 80%;
  z-index: 100;
  width: 800px;
}

.popup-container.visible {
  transform: translate(-50%, -50%) scale(1);
  opacity: 1;
}

.popup-title {
  font-size: 28px;
  color: #2196f3;
  margin-bottom: 20px;
  text-align: center;
}

.popup-content {
  font-size: 24px;
  line-height: 1.8;
  color: #333;
}

.popup-highlight {
  background: #fff3b0;
  padding: 2px 5px;
  border-radius: 3px;
  transition: all 0.3s ease;
}

.popup-highlight.active {
  background: #ffeb3b;
  transform: scale(1.05);
}

.practice-subtitle {
  font-size: 28px;
  color: #333;
  text-align: left;
  margin: 0;
  position: absolute;
  top: 120px;
  left: 140px;
}

.example-container {
  display: grid;
  grid-template-columns: 1fr;
  gap: 20px;
  width: 100%;
  max-width: 800px;
  margin: 0 auto;
  opacity: 0;
  transform: translateY(20px);
  transition: all 0.5s ease;
}

.example-container.visible {
  opacity: 1;
  transform: translateY(0);
}

.example {
  font-size: 28px;
  padding: 15px;
  margin: 10px;
  background: rgba(255, 255, 255, 0.9);
  border-radius: 10px;
  box-shadow: 0 2px 5px rgba(0, 0, 0, 0.1);
  opacity: 0;
  transform: translateY(20px);
  transition: all 0.5s ease;
}

.example.visible {
  opacity: 1;
  transform: translateY(0);
}

.highlight {
  padding: 0 5px;
  border-radius: 3px;
  transition: all 0.3s ease;
}

.highlight.active {
  background-color: #ffeb3b;
  transform: scale(1.05);
}

.controls {
  position: fixed;
  bottom: 20px;
  right: 20px;
  z-index: 1000;
  display: flex;
  gap: 10px;
}

button {
  padding: 12px 24px;
  font-size: 18px;
  background: #2196f3;
  color: #fff;
  border: none;
  border-radius: 5px;
  cursor: pointer;
  transition: all 0.3s ease;
}

button:hover {
  background: #1976d2;
}

#prevButton,
#nextButton {
  background: #4caf50;
}

#prevButton:hover,
#nextButton:hover {
  background: #45a049;
}

#prevButton:disabled,
#nextButton:disabled {
  background: #ccc;
  cursor: not-allowed;
}

.progress-bar {
  position: fixed;
  top: 0;
  left: 0;
  height: 5px;
  background: #2196f3;
  width: 0%;
  transition: width 0.3s ease;
  z-index: 1000;
}

.text-item {
  opacity: 0;
  transform: translateY(20px);
  transition: all 0.5s ease;
}

.text-item.visible {
  opacity: 1;
  transform: translateY(0);
}

.badge {
  position: absolute;
  left: 50px;
  top: 82px;
  width: 250px;
  text-align: center;
  font-family: 'Comic Sans MS', cursive, sans-serif;
  font-size: 18px;
}

.options {
  display: flex;
  gap: 30px;
  justify-content: center;
  margin: 30px 0;
}

.option {
  padding: 15px 30px;
  font-size: 28px;
  background: #fff;
  border: 2px solid #2196f3;
  border-radius: 10px;
  color: #2196f3;
  cursor: pointer;
  opacity: 0;
  transform: translateY(20px);
  transition: all 0.5s ease;
}

.option.visible {
  opacity: 1;
  transform: translateY(0);
}

.option.highlight {
  background: #4caf50;
  color: white;
  border-color: #4caf50;
  transform: scale(1.1);
}

.question {
  font-size: 32px;
  text-align: center;
  margin-bottom: 30px;
}

.answer {
  font-size: 28px;
  text-align: center;
  margin-top: 20px;
}