* {
    box-sizing: border-box;
    margin: 0;
    padding: 0;
    font-family: system-ui, sans-serif;
  }
  
  body {
    display: flex;
    flex-direction: column;
    align-items: center;
    gap: 1.5rem;
    padding: 1rem;
    max-width: 960px;
    margin-inline: auto;
  }
  
  header {
    text-align: center;
  }
  
  #upload-section {
    display: flex;
    flex-wrap: wrap;
    gap: 2rem;
    justify-content: center;
    width: 100%;
  }
  
  .upload-wrapper {
    border: 2px dashed #aaa;
    border-radius: 0.75rem;
    padding: 1rem;
    flex: 1 1 280px;
    max-width: 420px;
    text-align: center;
  }

  .file-block {
    display: flex;
    flex-direction: column;
    align-items: center;
  }
  
  
  input[type="file"] {
    margin-block: 0.75rem;
  }
  
  #action-container {
    margin-top: 1rem;
  }
  
  button.generate-btn {
    padding: 0.5rem 1.25rem;
    font-size: 1.1rem;
    background: #1e88e5;
    color: #fff;
    border: none;
    border-radius: 0.5rem;
    cursor: pointer;
  }
  button.generate-btn:disabled {
    opacity: 0.6;
    cursor: not-allowed;
  }
  
  .loader {
    border: 4px solid #f3f3f3;
    border-top: 4px solid #1e88e5;
    border-radius: 50%;
    width: 42px;
    height: 42px;
    animation: spin 1s linear infinite;
    margin-inline: auto;
    margin-top: 1rem;
  }
  @keyframes spin {
    0% { transform: rotate(0deg); }
    100% { transform: rotate(360deg); }
  }
  
  #results {
    position: relative;
    width: 100%;
    margin-top: 2rem;
    display: flex;
    gap: 2rem;
    justify-content: flex-start;
    overflow-x: auto;
  }

  /* ─── RESULT LAYOUT ───────────────────────────────── */
  #result-layout{
    display:flex;
    justify-content:center;
    align-items:center;
    position:relative;
    width:100%;
    padding:2rem 0;
    gap:clamp(3rem,8vw,6rem);   /*   ⬅︎ lớn hơn ⇒ label + line không bị chạm   */
    overflow-x:auto;            /*   nếu màn nhỏ sẽ scroll ngang   */
  }

  /* Tester đứng giữa cột trái */
  #tester-column{
    display:flex;
    justify-content:center;
    align-items:center;
  }

  /* Sampler xếp cột phải */
  #sampler-column{
    display:flex;
    flex-direction:column;
    gap:2.5rem;                 /*   giãn từng ảnh   */
    align-items:center;
  }

  /* Ảnh vuông */
  .square{
    width:120px;
    height:120px;
    border-radius:0.5rem;
    overflow:hidden;
    flex-shrink:0;
  }
  .square img{width:100%;height:100%;object-fit:cover}

  /* Canvas + nhãn */
  #lines-canvas{position:absolute;top:0;left:0;pointer-events:none;z-index:0}
  .label{position:absolute;transform:translate(-50%,-50%);z-index:1}

  /* ─── MOBILE ≤600 px: giữ hai cột nhưng thu nhỏ ảnh ─── */
  @media (max-width:600px){
    #result-layout{gap:2rem}         /*   hẹp lại   */
    .square{width:72px;height:72px;} /*   nhỏ hơn   */
  }

    .tester-node {
      box-shadow: 0 0 10px rgba(59,130,246,0.5);
    }