Styling

Every object that holds cells — a cell, a range, a row, a column, a worksheet, the workbook itself — exposes a Style property of the same type, IXLStyle. Setting a style on a range applies it to every cell in that range; setting it on the workbook changes the default for everything.

IXLStyle has six parts:

Part	Controls
`Font`	Typeface, size, weight, colour, underline, super/subscript
`Fill`	Background colour and pattern
`Border`	Line style and colour on each edge, plus diagonals
`Alignment`	Horizontal/vertical placement, wrapping, indent, rotation
`NumberFormat`	How numbers are displayed
`Protection`	Whether the cell is locked or hidden when the sheet is protected

Applying a style

var ws = workbook.Worksheet("Report");

// One cell
ws.Cell("A1").Style.Font.Bold = true;

// A range — applies to all cells in it
ws.Range("A1:D1").Style.Font.Bold = true;

// A whole column or row
ws.Column("B").Style.NumberFormat.Format = "#,##0.00";
ws.Row(1).Style.Fill.BackgroundColor = XLColor.LightGray;

// The whole sheet
ws.Style.Font.FontName = "Calibri";

// The workbook default — every new cell inherits this
workbook.Style.Font.FontSize = 11;

Every setter also has a fluent Set… form that returns the style, so a block of related settings reads as one statement:

ws.Range("A1:D1").Style
    .Font.SetBold()
    .Font.SetFontColor(XLColor.White)
    .Fill.SetBackgroundColor(XLColor.FromHtml("#FF4F81BD"))
    .Alignment.SetHorizontal(XLAlignmentHorizontalValues.Center)
    .Border.SetBottomBorder(XLBorderStyleValues.Thin);

Reusing a style

Build a style once from workbook.Style and assign it wherever it is needed. This is both tidier and cheaper than repeating the property sets, because XLibur interns identical styles:

var headerStyle = workbook.Style;
headerStyle.Font.Bold = true;
headerStyle.Font.FontColor = XLColor.White;
headerStyle.Fill.BackgroundColor = XLColor.FromHtml("#FF4F81BD");
headerStyle.Alignment.Horizontal = XLAlignmentHorizontalValues.Center;

ws.Range("A1:F1").Style = headerStyle;
ws.Range("A20:F20").Style = headerStyle;

tip

Style whole columns or ranges rather than looping over cells. A single ws.Range("D2:D10000").Style.NumberFormat.Format = "0.00" stores one style; a loop over 10,000 cells does 10,000 assignments to reach the same result.

Font

var style = ws.Cell("B2").Style;

style.Font.FontName = "Segoe UI";
style.Font.FontSize = 14;
style.Font.Bold = true;
style.Font.Italic = true;
style.Font.Underline = XLFontUnderlineValues.Single;   // None, Single, Double, SingleAccounting, DoubleAccounting
style.Font.Strikethrough = true;
style.Font.FontColor = XLColor.DarkRed;
style.Font.VerticalAlignment = XLFontVerticalTextAlignmentValues.Superscript;  // or Subscript, Baseline

Fluent equivalent:

ws.Cell("B2").Style
    .Font.SetFontName("Segoe UI")
    .Font.SetFontSize(14)
    .Font.SetBold()
    .Font.SetFontColor(XLColor.DarkRed);

Fonts follow the workbook theme when you use FontScheme, which keeps text in step with whatever theme fonts the file carries:

ws.Cell("A1").Style.Font.FontScheme = XLFontScheme.Major;   // heading font
ws.Cell("A2").Style.Font.FontScheme = XLFontScheme.Minor;   // body font

Rich text — mixed formatting in one cell

When a single cell needs more than one format, write rich text instead of a plain value:

var cell = ws.Cell("A1");
cell.GetRichText()
    .AddText("Total: ").SetFontColor(XLColor.Gray)
    .AddText("1,240").SetBold().SetFontColor(XLColor.DarkGreen)
    .AddText(" units");

Background colour

Fill is the cell background. In almost every case you want a solid fill, which XLibur sets for you when you assign a background colour:

ws.Cell("A1").Style.Fill.BackgroundColor = XLColor.Yellow;
ws.Range("A1:D1").Style.Fill.SetBackgroundColor(XLColor.FromHtml("#FFEEECE1"));

Patterned fills need all three properties:

var style = ws.Cell("B2").Style;
style.Fill.PatternType = XLFillPatternValues.LightGrid;
style.Fill.BackgroundColor = XLColor.White;
style.Fill.PatternColor = XLColor.LightBlue;

Specifying colours

XLColor accepts named colours, HTML hex, ARGB components, Excel's indexed palette, and theme colours:

XLColor.Red                                  // one of ~140 named colours
XLColor.FromName("CornflowerBlue")
XLColor.FromHtml("#FF4F81BD")                // AARRGGBB or RRGGBB
XLColor.FromArgb(0x4F, 0x81, 0xBD)           // r, g, b
XLColor.FromArgb(255, 0x4F, 0x81, 0xBD)      // a, r, g, b
XLColor.FromIndex(44)                        // legacy indexed palette
XLColor.FromTheme(XLThemeColor.Accent1)      // follows the workbook theme
XLColor.FromTheme(XLThemeColor.Accent1, 0.4) // theme colour, lightened

Theme colours are the ones to reach for when you want the workbook to stay coherent — see Theming.

Borders

Each edge has a style and a colour:

var style = ws.Cell("B2").Style;

style.Border.TopBorder = XLBorderStyleValues.Thin;
style.Border.TopBorderColor = XLColor.Black;
style.Border.BottomBorder = XLBorderStyleValues.Double;
style.Border.BottomBorderColor = XLColor.Black;
style.Border.LeftBorder = XLBorderStyleValues.Thin;
style.Border.RightBorder = XLBorderStyleValues.Thin;

Available line styles: None, Hair, Dotted, DashDotDot, DashDot, Dashed, Thin, MediumDashDotDot, SlantDashDot, MediumDashDot, MediumDashed, Medium, Thick, Double.

Outside and inside borders

On a range, OutsideBorder draws the perimeter and InsideBorder draws the grid between cells. This is the concise way to box a table:

var range = ws.Range("A1:D10");

range.Style.Border.OutsideBorder = XLBorderStyleValues.Medium;
range.Style.Border.OutsideBorderColor = XLColor.Black;
range.Style.Border.InsideBorder = XLBorderStyleValues.Thin;
range.Style.Border.InsideBorderColor = XLColor.LightGray;

note

OutsideBorder and InsideBorder are write-only — they are a shorthand that expands into the individual edge settings, so there is nothing meaningful to read back.

Diagonal borders

var style = ws.Cell("B2").Style;
style.Border.DiagonalBorder = XLBorderStyleValues.Thin;
style.Border.DiagonalBorderColor = XLColor.Red;
style.Border.DiagonalUp = true;      // bottom-left to top-right
style.Border.DiagonalDown = true;    // top-left to bottom-right

Alignment and orientation

var style = ws.Cell("B2").Style;

style.Alignment.Horizontal = XLAlignmentHorizontalValues.Center;
style.Alignment.Vertical = XLAlignmentVerticalValues.Center;
style.Alignment.WrapText = true;
style.Alignment.ShrinkToFit = false;
style.Alignment.Indent = 2;

Horizontal values: General, Left, Center, Right, Fill, Justify, CenterContinuous, Distributed. Vertical values: Top, Center, Bottom, Justify, Distributed.

Text rotation

TextRotation is in degrees, from -90 (rotated clockwise) to 90 (counterclockwise). The special value 255 stacks the characters vertically:

// Angled column headers — the classic use
ws.Range("B1:H1").Style.Alignment.TextRotation = 45;
ws.Row(1).Height = 60;

ws.Cell("A5").Style.Alignment.TextRotation = -90;   // read bottom-to-top
ws.Cell("A6").Style.Alignment.TextRotation = 255;   // stacked letters

TopToBottom is a separate switch that lays the text out downwards rather than rotating it:

ws.Cell("A7").Style.Alignment.TopToBottom = true;

Reading order

For right-to-left content:

ws.Cell("A1").Style.Alignment.ReadingOrder = XLAlignmentReadingOrderValues.RightToLeft;
ws.RightToLeft = true;   // flips the whole sheet

Number formats

Two ways to set a format — a custom format string, or one of Excel's built-in format IDs:

ws.Range("D2:D100").Style.NumberFormat.Format = "$ #,##0.00";
ws.Range("E2:E100").Style.NumberFormat.Format = "0.00%";
ws.Range("F2:F100").Style.NumberFormat.Format = "yyyy-MM-dd";
ws.Range("G2:G100").Style.NumberFormat.Format = "[h]:mm:ss";

// Built-in format IDs — 15 is "d-mmm-yy", 3 is "#,##0"
ws.Column("C").Style.NumberFormat.NumberFormatId = 15;
ws.Column("H").Style.NumberFormat.NumberFormatId = (int)XLPredefinedFormat.Number.IntegerWithSeparator;

Some formats worth keeping to hand:

Format string	Renders `1234.5` as
`#,##0`	`1,235`
`#,##0.00`	`1,234.50`
`$ #,##0.00`	`$ 1,234.50`
`0.00%`	`123450.00%`
`0.00E+00`	`1.23E+03`
`#,##0;[Red](#,##0)`	`1,235` — negatives red and parenthesised
`yyyy-mm-dd hh:mm`	(dates) `2026-01-21 09:30`
`[h]:mm:ss`	(durations) elapsed hours beyond 24

There is also a DateFormat shortcut, which is the same underlying property scoped to dates:

ws.Range("C2:C100").Style.DateFormat.Format = "dd/MM/yyyy";

note

A number format changes only how a value is displayed. GetDouble() still returns the raw number; use GetFormattedString() to read it as the user sees it.

Protection

Locking only takes effect once the sheet itself is protected:

ws.Style.Protection.Locked = true;                      // default for all cells
ws.Range("B2:B10").Style.Protection.Locked = false;     // leave these editable
ws.Range("C2:C10").Style.Protection.Hidden = true;      // hide formulas in the formula bar

ws.Protect("s3cret");

A worked example

using XLibur.Excel;

using var workbook = new XLWorkbook();
var ws = workbook.Worksheets.Add("Sales");

string[] headers = ["Region", "Q1", "Q2", "Q3", "Q4", "Total"];
for (var i = 0; i < headers.Length; i++)
{
    ws.Cell(1, i + 1).Value = headers[i];
}

var data = new[]
{
    ("North", 12000d, 13500d, 12800d, 15100d),
    ("South", 9800d, 10200d, 11000d, 11900d),
    ("East", 15300d, 14100d, 16200d, 17400d),
    ("West", 7400d, 8100d, 7900d, 8600d),
};

var row = 2;
foreach (var (region, q1, q2, q3, q4) in data)
{
    ws.Cell(row, 1).Value = region;
    ws.Cell(row, 2).Value = q1;
    ws.Cell(row, 3).Value = q2;
    ws.Cell(row, 4).Value = q3;
    ws.Cell(row, 5).Value = q4;
    ws.Cell(row, 6).FormulaA1 = $"=SUM(B{row}:E{row})";
    row++;
}

var lastRow = row - 1;

// Header band
ws.Range(1, 1, 1, 6).Style
    .Font.SetBold()
    .Font.SetFontColor(XLColor.White)
    .Fill.SetBackgroundColor(XLColor.FromHtml("#FF4F81BD"))
    .Alignment.SetHorizontal(XLAlignmentHorizontalValues.Center);

// Money columns
ws.Range(2, 2, lastRow, 6).Style.NumberFormat.Format = "$ #,##0";

// Emphasise the totals column
ws.Range(1, 6, lastRow, 6).Style.Font.Bold = true;

// Box the table
var table = ws.Range(1, 1, lastRow, 6);
table.Style.Border.OutsideBorder = XLBorderStyleValues.Medium;
table.Style.Border.InsideBorder = XLBorderStyleValues.Thin;
table.Style.Border.InsideBorderColor = XLColor.LightGray;

ws.Columns().AdjustToContents();
workbook.SaveAs("StyledSales.xlsx");

Where to next

Theming — theme colours so styles stay consistent across a workbook
Conditional Formatting — styles driven by cell values
Tables — built-in table styles, no manual banding required

Applying a style​

Reusing a style​

Font​

Rich text — mixed formatting in one cell​

Background colour​

Specifying colours​

Borders​

Outside and inside borders​

Diagonal borders​

Alignment and orientation​

Text rotation​

Reading order​

Number formats​

Protection​

A worked example​

Where to next​