:root {
        --max-width: 640px;
        --gap: 12px;
        --radius: 12px;
}

* { box-sizing: border-box; }

body {
        margin: 0;
        font-family: Helvetica, Arial, sans-serif;
        line-height: 1.45;
        color: #111;
        background: #f7f7f8;
        -webkit-font-smoothing: antialiased;
        -moz-osx-font-smoothing: grayscale;
      }

      .container {
        
        margin: 0 auto;
        padding: 16px clamp(12px, 3vw, 20px) 28px;
      }

      header { text-align: center; margin-bottom: 12px; }
      h2#problem-title { margin: 0 0 8px; font-weight: 700; }

      .board-wrap {
        display: grid;
        place-items: center;
        margin: 8px 0 12px;
      }

      /* Доска — всегда квадрат */
      #board {
        width: 100%;
        max-width: 768px;      
        aspect-ratio: 1 / 1;
        opacity: 1;
        border-radius: var(--radius);
        background: #fff;
        box-shadow: 0 1px 2px rgba(0, 0, 0, 0.04);
        }
      .controls {
        display: flex;
        flex-wrap: wrap;
        align-items: center;
        justify-content: center;
        gap: var(--gap);
        margin: 12px 0 4px;
      }

      .controls input[type="text"],
      .controls input[type="number"] {
        width: 140px;
        padding: 10px 12px;
        border: 1px solid #d7d7db;
        border-radius: 10px;
        background: #fff;
        font-size: 16px; /* избегаем зума на iOS */
      }

      .btn {
        padding: 10px 14px;
        border: 1px solid #d7d7db;
        border-radius: 10px;
        background: #fff;
        cursor: pointer;
        font-size: 16px;
        transition: transform .02s ease, background .15s ease, border-color .15s ease;
        touch-action: manipulation;
      }
      .btn:active { transform: translateY(1px); }
      .btn-primary {
        background: #111827;
        color: #fff;
        border-color: #111827;
      }

      .info {
        max-width: var(--max-width);
        margin: 12px auto 0; 
        text-align: center;
        margin-top: 14px;
        color: #222;
      }
      .info p { margin: 8px 0; }

      .card {
        background: #fff;
        border: 1px solid #e6e6ea;
        border-radius: var(--radius);
        padding: 12px 14px;
        display: inline-block;
        text-align: left;
      }

      a { color: #2563eb; text-decoration: none; }
      a:hover { text-decoration: underline; }

      
      @media (max-width: 560px) {
        h2#problem-title { font-size: 18px; }
        .controls {
          justify-content: stretch;
        }
        .controls > * {
          flex: 1 1 100%;
        }
        .controls input {
          width: 100%;
        }
        .btn,
        .btn-primary {
          width: 100%;
        }
        .card { width: 100%; }
      }

      
      @media (prefers-color-scheme: dark) {
        body { background: #0b0b0c; color: #eaeaea; }
        #board, .card, .controls input { background: #151517; border-color: #2a2a2e; color: #eaeaea; }
        .btn { background: #1b1b1f; border-color: #2a2a2e; color: #eaeaea; }
        .btn-primary { background: #2563eb; border-color: #2563eb; color: #fff; }
        a { color: #8ab4ff; }
      }

.gallery { 
  max-width: 1000px; 
  margin: 12px auto 0; 
  padding: 0 4px; 
}

.gallery-main {
  display: flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  margin-bottom: 10px;
}

.gallery-main .nav {
  appearance: none;
  border: 1px solid #d7d7db;
  background: #fff;
  border-radius: 999px;
  width: 36px; height: 36px;
  font-size: 20px; line-height: 1;
  cursor: pointer;
}
.gallery-main .nav:active { transform: translateY(1px); }

.gallery-main .main-link {
  display: block;
  max-width: 100%;
  flex: 1 1 auto;
}
#main-image {
  display: block;
  width: 100%;
  max-height: 60vh;         
  object-fit: contain;
  border-radius: var(--radius);
  background: #fff;
  border: 1px solid #e6e6ea;
  box-shadow: 0 1px 2px rgba(0,0,0,.04);
}

.thumbs {
  display: flex;
  gap: 8px;
  overflow-x: auto;
  padding-bottom: 4px;
  -webkit-overflow-scrolling: touch;
}
.thumbs .thumb {
  flex: 0 0 auto;
  border: 1px solid #d7d7db;
  border-radius: 10px;
  background: #fff;
  padding: 2px;
  cursor: pointer;
  transition: border-color .15s ease, transform .02s ease;
}
.thumbs .thumb:active { transform: translateY(1px); }
.thumbs .thumb.is-active { border-color: #2563eb; }
.thumbs img {
  display: block;
  width: 84px; height: 84px;
  object-fit: cover;
  border-radius: 8px;
}

@media (max-width: 560px) {
  #main-image { max-height: 50vh; }
}

/* Dark */
@media (prefers-color-scheme: dark) {
  .gallery-main .nav { background: #1b1b1f; border-color: #2a2a2e; color: #eaeaea; }
  #main-image { background: #151517; border-color: #2a2a2e; }
  .thumbs .thumb { background: #151517; border-color: #2a2a2e; }
  .thumbs .thumb.is-active { border-color: #8ab4ff; }
}