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(+1)

If anybody is googling for this later:

    <style>
      html, body
      {
        height: 100%;
        margin: 0;
      }
      body
      {
        display: flex;
        display: -webkit-flex;
        -webkit-justify-content: center;
                justify-content: center;
        -webkit-align-items: center;
                align-items: center;  
      }
      canvas
      {
        display: block;
        outline: none;
        height: 100%;
        max-height: 133.333vw;
        width: 100%;
        max-width: 75vh;
      }
      </style>

worked well for my use case