<svg width="8cm" height="4cm">
     <defs>
          <pattern id="TrianglePattern" x="0" y="0" width="1cm" height="1cm" viewBox="0 0 10 10">
               <path d="M 0 0 L 7 0 L 3.5 7 z" style="fill:red; stroke:blue"/>
          </pattern>
     </defs>
     <rect style="fill:none; stroke:blue" x=".01cm" y=".01cm" width="7.98cm" height="3.98cm"/>
     <ellipse style="fill:url(#TrianglePattern); stroke:black" cx="4cm" cy="2cm" rx="3.5cm" ry="1.5cm"/>
</svg>