a:txSp (Text Shape)

<p:txSp xmlns:p="http://schemas.openxmlformats.org/presentationml/2006/main" xmlns:a="http://schemas.openxmlformats.org/drawingml/2006/main">
  <p:nvTxSpPr>
    <p:cNvPr id="1" name="Text Box 1"/>
    <p:cNvTxSpPr/>
    <p:nvPr/>
  </p:nvTxSpPr>
  <p:txSpPr>
    <a:xfrm>
      <a:off x="1000" y="1000"/>
      <a:ext cx="2000000" cy="1000000"/>
    </a:xfrm>
    <a:prstGeom prst="rect">
      <a:avLst/>
    </a:prstGeom>
    <a:solidFill>
      <a:srgbClr val="E7E6E6"/>
    </a:solidFill>
    <a:ln w="9525">
      <a:solidFill>
        <a:srgbClr val="595959"/>
      </a:solidFill>
    </a:ln>
  </p:txSpPr>
  <p:txBody>
    <a:bodyPr/>
    <a:lstStyle/>
    <a:p>
      <a:r>
        <a:rPr lang="en-US" sz="2400" b="0"/>
        <a:t>Sample Text</a:t>
      </a:r>
    </a:p>
  </p:txBody>
</p:txSp>

using DocumentFormat.OpenXml.Presentation;
using DocumentFormat.OpenXml.Drawing;

var txSp = new Shape();

var nvTxSpPr = new NonVisualShapeProperties();
nvTxSpPr.Append(new NonVisualDrawingProperties { Id = 1, Name = "Text Box 1" });
nvTxSpPr.Append(new NonVisualShapeDrawingProperties());
nvTxSpPr.Append(new ShapeNonVisualProperties());
txSp.Append(nvTxSpPr);

var txSpPr = new ShapeProperties();
var xfrm = new Transform2D();
xfrm.Append(new Offset { X = 1000, Y = 1000 });
xfrm.Append(new Extents { Cx = 2000000, Cy = 1000000 });
txSpPr.Append(xfrm);

var prstGeom = new PresetGeometry { Preset = ShapeTypeValues.Rectangle };
prstGeom.Append(new AdjustmentValueList());
txSpPr.Append(prstGeom);

var solidFill = new SolidFill();
solidFill.Append(new RgbColorModelHex { Val = "E7E6E6" });
txSpPr.Append(solidFill);

var ln = new Outline { Width = 9525 };
var lineFill = new SolidFill();
lineFill.Append(new RgbColorModelHex { Val = "595959" });
ln.Append(lineFill);
txSpPr.Append(ln);

var txBody = new TextBody();
txBody.Append(new BodyProperties());
txBody.Append(new ListStyle());
var p = new Paragraph();
var r = new Run();
r.Append(new RunProperties { Language = "en-US", FontSize = 2400 });
r.Append(new Text { Text = "Sample Text" });
p.Append(r);
txBody.Append(p);
txSp.Append(txBody);

<p:txSp xmlns:p="http://schemas.openxmlformats.org/presentationml/2006/main" xmlns:a="http://schemas.openxmlformats.org/drawingml/2006/main">
  <p:nvTxSpPr>
    <p:cNvPr id="2" name="Formatted Text"/>
    <p:cNvTxSpPr/>
    <p:nvPr/>
  </p:nvTxSpPr>
  <p:txSpPr>
    <a:xfrm>
      <a:off x="2000000" y="2000000"/>
      <a:ext cx="3000000" cy="1500000"/>
    </a:xfrm>
    <a:prstGeom prst="rect">
      <a:avLst/>
    </a:prstGeom>
    <a:gradFill>
      <a:gsLst>
        <a:gs pos="0">
          <a:srgbClr val="0070C0"/>
        </a:gs>
        <a:gs pos="100000">
          <a:srgbClr val="002060"/>
        </a:gs>
      </a:gsLst>
      <a:lin ang="5400000" scaled="1"/>
    </a:gradFill>
  </p:txSpPr>
  <p:txBody>
    <a:bodyPr/>
    <a:lstStyle/>
    <a:p>
      <a:pPr algn="ctr"/>
      <a:r>
        <a:rPr lang="en-US" sz="3200" b="1" color="FFFFFF"/>
        <a:t>Title Text</a:t>
      </a:r>
    </a:p>
  </p:txBody>
</p:txSp>

var txSp = new Shape();

// Non-visual properties
var nvTxSpPr = new NonVisualShapeProperties();
nvTxSpPr.Append(new NonVisualDrawingProperties { Id = 2, Name = "Formatted Text" });
nvTxSpPr.Append(new NonVisualShapeDrawingProperties());
nvTxSpPr.Append(new ShapeNonVisualProperties());
txSp.Append(nvTxSpPr);

// Text shape properties with gradient
var txSpPr = new ShapeProperties();
var xfrm = new Transform2D();
xfrm.Append(new Offset { X = 2000000, Y = 2000000 });
xfrm.Append(new Extents { Cx = 3000000, Cy = 1500000 });
txSpPr.Append(xfrm);

var prstGeom = new PresetGeometry { Preset = ShapeTypeValues.Rectangle };
prstGeom.Append(new AdjustmentValueList());
txSpPr.Append(prstGeom);

var gradFill = new GradientFill();
var gsLst = new GradientStopList();
var gs1 = new GradientStop { Position = 0 };
gs1.Append(new RgbColorModelHex { Val = "0070C0" });
gsLst.Append(gs1);
var gs2 = new GradientStop { Position = 100000 };
gs2.Append(new RgbColorModelHex { Val = "002060" });
gsLst.Append(gs2);
gradFill.Append(gsLst);
gradFill.Append(new LinearGradientFillProperties { Angle = 5400000, Scaled = true });
txSpPr.Append(gradFill);
txSp.Append(txSpPr);

// Text body with formatted text
var txBody = new TextBody();
txBody.Append(new BodyProperties());
txBody.Append(new ListStyle());
var p = new Paragraph { ParagraphProperties = new ParagraphProperties { Alignment = TextAlignmentTypeValues.Center } };
var r = new Run();
r.Append(new RunProperties { Language = "en-US", FontSize = 3200, Bold = true, Color = "FFFFFF" });
r.Append(new Text { Text = "Title Text" });
p.Append(r);
txBody.Append(p);
txSp.Append(txBody);