/* The container that holds ONLY the radicand (under the root). 
   Not wrapping the √ sign. */
   .radicand-container {
    display: inline-block;
    vertical-align: bottom;
    border: 1px solid transparent; /* Hidden border by default */
    margin: 0 3px;
    transition: border-color 0.2s;
  }
  
  /* When the user is focused inside the radicand, show highlight */
  .radicand-container.radicand-active {
    border-color: #000;     /* visible border */
    background-color: #f9f9f9; /* optional highlight color */
  }
  
  /* The editable radicand. 
     We'll display a top border to simulate the 'overbar'.
     The bounding box can be obvious or subtle – your choice.
  */
  .radicand {
    min-width: 30px;
    min-height: 1em;
    border-top: 1px solid #000;   /* overbar */
    padding: 2px 4px;
    margin-top: 2px;
    box-sizing: border-box;
    outline: none;     /* remove default focus outline */
    display: inline-block;
    font-size: 1em;
  }