:root {
  --primary-color: #3498db;
  --secondary-color: #2ecc71;
  --background-color: #ffffff;
  --text-color: #333333;
  --header-bg: #f0f0f0;
  
  --fs-small: 0.875rem;
  --fs-medium: 1rem;
  --fs-large: 1.25rem;
  --fs-xlarge: 1.5rem;
  
  --space-small: 0.5rem;
  --space-medium: 1rem;
  --space-large: 1.5rem;
  
  --font-primary: 'Arial', sans-serif;
  
  --border-radius: 4px;
  --transition-duration: 0.3s;
}

.dark-theme {
  --background-color: #333333;
  --text-color: #ffffff;
  --header-bg: #222222;
}

body {
  font-family: var(--font-primary);
  background-color: var(--background-color);
  color: var(--text-color);
  transition: background-color var(--transition-duration), color var(--transition-duration);
  margin: 0;
  padding: 0;
}

.page__container {
  max-width: 1200px;
  margin: 0 auto;
  padding: var(--space-large);
}

.header {
  text-align: center;
  margin-bottom: var(--space-large);
  background-color: var(--header-bg);
  padding: var(--space-medium);
}

.header__title {
  font-size: var(--fs-xlarge);
  color: var(--primary-color);
}

.header__subtitle {
  font-size: var(--fs-medium);
  color: var(--secondary-color);
}

.theme-switcher {
  display: flex;
  justify-content: center;
  gap: var(--space-medium);
  margin-top: var(--space-large);
}

.theme-switcher__btn {
  padding: var(--space-small) var(--space-medium);
  font-size: var(--fs-small);
  border: none;
  border-radius: var(--border-radius);
  cursor: pointer;
  transition: background-color var(--transition-duration);
}

.theme-switcher__btn--light {
  background-color: var(--background-color);
  color: var(--text-color);
}

.theme-switcher__btn--dark {
  background-color: var(--text-color);
  color: var(--background-color);
}

.color-picker {
  display: flex;
  justify-content: center;
  gap: var(--space-medium);
  margin-top: var(--space-large);
}

.color-picker__input {
  width: 50px;
  height: 50px;
  border: none;
  border-radius: 50%;
  overflow: hidden;
  cursor: pointer;
}

.gallery {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(250px, 1fr));
  gap: var(--space-large);
}

.gallery__item {
  overflow: hidden;
  border-radius: var(--border-radius);
}

.progressive-image {
  position: relative;
  padding-bottom: 75%; /* 4:3 Aspect Ratio */
}

.progressive-image__loading,
.progressive-image__overlay {
  position: absolute;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  background-size: cover;
  background-position: center;
}

.progressive-image__loading {
  filter: blur(10px);
}

.progressive-image__overlay {
  opacity: 0;
  transition: opacity var(--transition-duration);
}

.progressive-image--loaded .progressive-image__overlay {
  opacity: 1;
}

@media (max-width: 768px) {
  .gallery {
    grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
  }
  
  .header__title {
    font-size: var(--fs-large);
  }
  
  .header__subtitle {
    font-size: var(--fs-small);
  }
}