minify/css/css.go at master · boomhut/minify

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// Package css minifies CSS3 following the specifications at http://www.w3.org/TR/css-syntax-3/.
package css
	"github.com/tdewolff/minify/v2"
	"github.com/tdewolff/parse/v2"
	"github.com/tdewolff/parse/v2/css"
	strconvParse "github.com/tdewolff/parse/v2/strconv"
	spaceBytes        = []byte(" "
8000
)
	colonBytes        = []byte(":")
	semicolonBytes    = []byte(";")
	commaBytes        = []byte(",")
	leftBracketBytes  = []byte("{")
	rightBracketBytes = []byte("}")
	rightParenBytes   = []byte(")")
	urlBytes          = []byte("url(")
	zeroBytes         = []byte("0")
	transparentBytes  = []byte("transparent")
	blackBytes        = []byte("#0000")
	initialBytes      = []byte("initial")
	noneBytes         = []byte("none")
	autoBytes         = []byte("auto")
	leftBytes         = []byte("left")
	topBytes          = []byte("top")
	n400Bytes         = []byte("400")
	n700Bytes         = []byte("700")
	n50pBytes         = []byte("50%")
	n100pBytes        = []byte("100%")
	repeatXBytes      = []byte("repeat-x")
	repeatYBytes      = []byte("repeat-y")
	importantBytes    = []byte("!important")
	dataSchemeBytes   = []byte("data:")
type cssMinifier struct {
	m *minify.M
	w io.Writer
	p *css.Parser
	o *Minifier
	tokenBuffer []Token
////////////////////////////////////////////////////////////////
// Minifier is a CSS minifier.
type Minifier struct {
	KeepCSS2     bool
	Precision    int // number of significant digits
	newPrecision int // precision for new numbers
// Minify minifies CSS data, it reads from r and writes to w.
func Minify(m *minify.M, w io.Writer, r io.Reader, params map[string]string) error {
	return (&Minifier{}).Minify(m, w, r, params)
// Token is a parsed token with extra information for functions.
type Token struct {
	css.TokenType
	Data       []byte
	Args       []Token // only filled for functions
	Fun, Ident Hash    // only filled for functions and identifiers respectively
func (t Token) String() string {
	if len(t.Args) == 0 {
		return t.TokenType.String() + "(" + string(t.Data) + ")"
	return fmt.Sprint(t.Args)
// Equal returns true if both tokens are equal.
func (t Token) Equal(t2 Token) bool {
	if t.TokenType == t2.TokenType && bytes.Equal(t.Data, t2.Data) && len(t.Args) == len(t2.Args) {
		for i := 0; i < len(t.Args); i++ {
			if t.Args[i].TokenType != t2.Args[i].TokenType || !bytes.Equal(t.Args[i].Data, t2.Args[i].Data) {
				return false
		return true
	return false
// IsZero return true if a dimension, percentage, or number token is zero.
func (t Token) IsZero() bool {
	// as each number is already minified, starting with a zero means it is zero
	return (t.TokenType == css.DimensionToken || t.TokenType == css.PercentageToken || t.TokenType == css.NumberToken) && t.Data[0] == '0'
// IsLength returns true if the token is a length.
func (t Token) IsLength() bool {
	if t.TokenType == css.DimensionToken {
		return true
	} else if t.TokenType == css.NumberToken && t.Data[0] == '0' {
		return true
	} else if t.TokenType == css.FunctionToken {
		fun := ToHash(t.Data[:len(t.Data)-1])
		if fun == Calc || fun == Min || fun == Max || fun == Clamp || fun == Attr || fun == Var || fun == Env {
			return true
	return false
// IsLengthPercentage returns true if the token is a length or percentage token.
func (t Token) IsLengthPercentage() bool {
	return t.TokenType == css.PercentageToken || t.IsLength()
////////////////////////////////////////////////////////////////
// Minify minifies CSS data, it reads from r and writes to w.
func (o *Minifier) Minify(m *minify.M, w io.Writer, r io.Reader, params map[string]string) error {
	o.newPrecision = o.Precision
	if o.newPrecision <= 0 || 15 < o.newPrecision {
		o.newPrecision = 15 // minimum number of digits a double can represent exactly
	z := parse.NewInput(r)
	defer z.Restore()
	isInline := params != nil && params["inline"] == "1"
	c := &cssMinifier{
		p: css.NewParser(z, isInline),
	c.minifyGrammar()
	if _, err := w.Write(nil); err != nil {
		return err
	if c.p.Err() == io.EOF {
		return nil
	return c.p.Err()
func (c *cssMinifier) minifyGrammar() {
	semicolonQueued := false
		gt, _, data := c.p.Next()
		switch gt {
		case css.ErrorGrammar:
			if c.p.HasParseError() {
				if semicolonQueued {
					c.w.Write(semicolonBytes)
				// write out the offending declaration (but save the semicolon)
				vals := c.p.Values()
				if len(vals) > 0 && vals[len(vals)-1].TokenType == css.SemicolonToken {
					vals = vals[:len(vals)-1]
					semicolonQueued = true
				for _, val := range vals {
					c.w.Write(val.Data)
				continue
		case css.EndAtRuleGrammar, css.EndRulesetGrammar:
			c.w.Write(rightBracketBytes)
			semicolonQueued = false
			continue
		if semicolonQueued {
			c.w.Write(semicolonBytes)
			semicolonQueued = false
		switch gt {
		case css.AtRuleGrammar:
			c.w.Write(data)
			values := c.p.Values()
			if ToHash(data[1:]) == Import && len(values) == 2 && values[1].TokenType == css.URLToken && 4 < len(values[1].Data) && values[1].Data[len(values[1].Data)-1] == ')' {
				url := values[1].Data
				if url[4] != '"' && url[4] != '\'' {
					a := 4
					for parse.IsWhitespace(url[a]) || parse.IsNewline(url[a]) {
					b := len(url) - 2
					for a < b && (parse.IsWhitespace(url[b]) || parse.IsNewline(url[b])) {
					if a == b {
						url = url[:2]
					} else {
						url = url[a-1 : b+2]
					url[0] = '"'
					url[len(url)-1] = '"'
				} else {
					url = url[4 : len(url)-1]
				values[1].Data = url
			for _, val := range values {
				c.w.Write(val.Data)
			semicolonQueued = true
		case css.BeginAtRuleGrammar:
			c.w.Write(data)
			for _, val := range c.p.Values() {
				c.w.Write(val.Data)
			c.w.Write(leftBracketBytes)
		case css.QualifiedRuleGrammar:
			c.minifySelectors(data, c.p.Values())
			c.w.Write(commaBytes)
		case css.BeginRulesetGrammar:
			c.minifySelectors(data, c.p.Values())
			c.w.Write(leftBracketBytes)
		case css.DeclarationGrammar:
			c.minifyDeclaration(data, c.p.Values())
			semicolonQueued = true
		case css.CustomPropertyGrammar:
			c.w.Write(data)
			c.w.Write(colonBytes)
			value := parse.TrimWhitespace(c.p.Values()[0].Data)
			if len(c.p.Values()[0].Data) != 0 && len(value) == 0 {
				value = spaceBytes
			c.w.Write(value)
			semicolonQueued = true
		case css.CommentGrammar:
			if len(data) > 5 && data[1] == '*' && data[2] == '!' {
				c.w.Write(data[:3])
				comment := parse.TrimWhitespace(parse.ReplaceMultipleWhitespace(data[3 : len(data)-2]))
				c.w.Write(comment)
				c.w.Write(data[len(data)-2:])
			c.w.Write(data)
func (c *cssMinifier) minifySelectors(property []byte, values []css.Token) {
	inAttr := false
	isClass := false
	for _, val := range c.p.Values() {
		if !inAttr {
			if val.TokenType == css.IdentToken {
				if !isClass {
					parse.ToLower(val.Data)
				isClass = false
			} else if val.TokenType == css.DelimToken && val.Data[0] == '.' {
				isClass = true
			} else if val.TokenType == css.LeftBracketToken {
				inAttr = true
			if val.TokenType == css.StringToken && len(val.Data) > 2 {
				s := val.Data[1 : len(val.Data)-1]
				if css.IsIdent(s) {
					c.w.Write(s)
					continue
			} else if val.TokenType == css.RightBracketToken {
				inAttr = false
			} else if val.TokenType == css.IdentToken && len(val.Data) == 1 && (val.Data[0] == 'i' || val.Data[0] == 'I') {
				c.w.Write(spaceBytes)
		c.w.Write(val.Data)
func (c *cssMinifier) parseFunction(values []css.Token) ([]Token, int) {
	level := 0
	args := []Token{}
	for ; i < len(values); i++ {
		tt := values[i].TokenType
		data := values[i].Data
		if tt == css.LeftParenthesisToken {
		} else if tt == css.RightParenthesisToken {
			if level == 0 {
		if tt == css.FunctionToken {
			subArgs, di := c.parseFunction(values[i:])
			h := ToHash(parse.ToLower(parse.Copy(data[:len(data)-1]))) // TODO: use ToHashFold
			args = append(args, Token{tt, data, subArgs, h, 0})
			i += di - 1
			var h Hash
			if tt == css.IdentToken {
				h = ToHash(parse.ToLower(parse.Copy(data))) // TODO: use ToHashFold
			args = append(args, Token{tt, data, nil, 0, h})
	return args, i
func (c *cssMinifier) parseDeclaration(values []css.Token) []Token {
	// Check if this is a simple list of values separated by whitespace or commas, otherwise we'll not be processing
	prevSep := true
	tokens := c.tokenBuffer[:0]
	for i := 0; i < len(values); i++ {
		tt := values[i].TokenType
		data := values[i].Data
		if tt == css.LeftParenthesisToken || tt == css.LeftBraceToken || tt == css.LeftBracketToken ||
			tt == css.RightParenthesisToken || tt == css.RightBraceToken || tt == css.RightBracketToken {
			return nil
		if !prevSep && tt != css.WhitespaceToken && tt != css.CommaToken && (tt != css.DelimToken || values[i].Data[0] != '/') {
			return nil
		if tt == css.WhitespaceToken || tt == css.CommaToken || tt == css.DelimToken && values[i].Data[0] == '/' {
			if tt != css.WhitespaceToken {
				tokens = append(tokens, Token{tt, data, nil, 0, 0})
			prevSep = true
		} else if tt == css.FunctionToken {
			args, di := c.parseFunction(values[i:])
			h := ToHash(parse.ToLower(parse.Copy(data[:len(data)-1]))) // TODO: use ToHashFold
			tokens = append(tokens, Token{tt, data, args, h, 0})
			prevSep = true
			i += di - 1
			var h Hash
			if tt == css.IdentToken {
				h = ToHash(parse.ToLower(parse.Copy(data))) // TODO: use ToHashFold
			tokens = append(tokens, Token{tt, data, nil, 0, h})
			prevSep = tt == css.URLToken
	c.tokenBuffer = tokens // update buffer size for memory reuse
	return tokens
func (c *cssMinifier) minifyDeclaration(property []byte, components []css.Token) {
	c.w.Write(property)
	c.w.Write(colonBytes)
	if len(components) == 0 {
	// Strip !important from the component list, this will be added later separately
	important := false
	if len(components) > 2 && components[len(components)-2].TokenType == css.DelimToken && components[len(components)-2].Data[0] == '!' && ToHash(components[len(components)-1].Data) == Important {
		components = components[:len(components)-2]
		important = true
	prop := ToHash(property)
	values := c.parseDeclaration(components)
	// Do not process complex values (eg. containing blocks or is not alternated between whitespace/commas and flat values
	if values == nil {
		if prop == Filter && len(components) == 11 {
			if bytes.Equal(components[0].Data, []byte("progid")) &&
				components[1].TokenType == css.ColonToken &&
				bytes.Equal(components[2].Data, []byte("DXImageTransform")) &&
				components[3].Data[0] == '.' &&
				bytes.Equal(components[4].Data, []byte("Microsoft")) &&
				components[5].Data[0] == '.' &&
				bytes.Equal(components[6].Data, []byte("Alpha(")) &&
				bytes.Equal(parse.ToLower(components[7].Data), []byte("opacity")) &&
				components[8].Data[0] == '=' &&
				components[10].Data[0] == ')' {
				components = components[6:]
				components[0].Data = []byte("alpha(")
		for _, component := range components {
			c.w.Write(component.Data)
		if important {
			c.w.Write(importantBytes)
	values = c.minifyTokens(prop, 0, values)
	if len(values) > 0 {
		values = c.minifyProperty(prop, values)
	c.writeDeclaration(values, important)
func (c *cssMinifier) writeFunction(args []Token) {
	for _, arg := range args {
		c.w.Write(arg.Data)
		if arg.TokenType == css.FunctionToken {
			c.writeFunction(arg.Args)
			c.w.Write(rightParenBytes)
func (c *cssMinifier) writeDeclaration(values []Token, important bool) {
	prevSep := true
	for _, value := range values {
		if !prevSep && value.TokenType != css.CommaToken && (value.TokenType != css.DelimToken || value.Data[0] != '/') {
			c.w.Write(spaceBytes)
		c.w.Write(value.Data)
		if value.TokenType == css.FunctionToken {
			c.writeFunction(value.Args)
			c.w.Write(rightParenBytes)
		if value.TokenType == css.CommaToken || value.TokenType == css.DelimToken && value.Data[0] == '/' || value.TokenType == css.FunctionToken || value.TokenType == css.URLToken {
			prevSep = true
			prevSep = false
	if important {
		c.w.Write(importantBytes)
func (c *cssMinifier) minifyTokens(prop Hash, fun Hash, values []Token) []Token {
	for i, value := range values {
		tt := value.TokenType
		switch tt {
		case css.NumberToken:
			if prop == Z_Index || prop == Counter_Increment || prop == Counter_Reset || prop == Orphans || prop == Widows {
				break // integers
			if c.o.KeepCSS2 {
				values[i].Data = minify.Decimal(values[i].Data, c.o.Precision) // don't use exponents
			} else {
				values[i].Data = minify.Number(values[i].Data, c.o.Precision)
		case css.PercentageToken:
			n := len(values[i].Data) - 1
			if c.o.KeepCSS2 {
				values[i].Data = minify.Decimal(values[i].Data[:n], c.o.Precision) // don't use exponents
			} else {
				values[i].Data = minify.Number(values[i].Data[:n], c.o.Precision)
			values[i].Data = append(values[i].Data, '%')
		case css.DimensionToken:
			var dim []byte
			values[i], dim = c.minifyDimension(values[i])
			if 1 < len(values[i].Data) && values[i].Data[0] == '0' && optionalZeroDimension[string(dim)] && prop != Flex && fun == 0 {
				// cut dimension for zero value, TODO: don't hardcode check for Flex and remove the dimension in minifyDimension
				values[i].Data = values[i].Data[:1]
		case css.StringToken:
			values[i].Data = removeMarkupNewlines(values[i].Data)
		case css.URLToken:
			if 10 < len(values[i].Data) {
				uri := parse.TrimWhitespace(values[i].Data[4 : len(values[i].Data)-1])
				delim := byte('"')
				if 1 < len(uri) && (uri[0] == '\'' || uri[0] == '"') {
					delim = uri[0]
					uri = removeMarkupNewlines(uri)
					uri = uri[1 : len(uri)-1]
				if 4 < len(uri) && parse.EqualFold(uri[:5], dataSchemeBytes) {
					uri = minify.DataURI(c.m, uri)
				if css.IsURLUnquoted(uri) {
					values[i].Data = append(append(urlBytes, uri...), ')')
				} else {
					values[i].Data = append(append(append(urlBytes, delim), uri...), delim, ')')
		case css.FunctionToken:
			values[i].Args = c.minifyTokens(prop, values[i].Fun, values[i].Args)
			fun := values[i].Fun
			args := values[i].Args
			if fun == Rgb || fun == Rgba || fun == Hsl || fun == Hsla {
				valid := true
				vals := []float64{}
				for i, arg := range args {
					numeric := arg.TokenType == css.NumberToken || arg.TokenType == css.PercentageToken
					separator := arg.TokenType == css.CommaToken || i != 5 && arg.TokenType == css.WhitespaceToken || i == 5 && arg.TokenType == css.DelimToken && arg.Data[0] == '/'
					if i%2 == 0 && !numeric || i%2 == 1 && !separator {
						valid = false
						break
					} else if numeric {
						var d float64
						if arg.TokenType == css.PercentageToken {
							var err error
							d, err = strconv.ParseFloat(string(arg.Data[:len(arg.Data)-1]), 32) // can overflow
							if err != nil {
								valid = false
								break
							d /= 100.0
							if d < minify.Epsilon {
							} else if 1.0-minify.Epsilon < d {
						} else {
							var err error
							d, err = strconv.ParseFloat(string(arg.Data), 32) // can overflow
							if err != nil {
								valid = false
								break
						vals = append(vals, d)
				if !valid {
				a := 1.0
				if len(vals) == 4 {
					if vals[0] < minify.Epsilon && vals[1] < minify.Epsilon && vals[2] < minify.Epsilon && vals[3] < minify.Epsilon {
						values[i] = Token{css.IdentToken, transparentBytes, nil, 0, Transparent}
						break
					} else if 1.0-minify.Epsilon < vals[3] {
						vals = vals[:3]
						values[i].Args = values[i].Args[:len(values[i].Args)-2]
						if fun == Rgba || fun == Hsla {
							values[i].Data = values[i].Data[:len(values[i].Data)-1]
							values[i].Data[len(values[i].Data)-1] = '('
					} else {
						a = vals[3]
				if a == 1.0 && (len(vals) == 3 || len(vals) == 4) { // only minify color if fully opaque
					if fun == Rgb || fun == Rgba {
						for j := 0; j < 3; j++ {
							if args[j*2].TokenType == css.NumberToken {
								vals[j] /= 255.0
								if vals[j] < minify.Epsilon {
									vals[j] = 0.0
								} else if 1.0-minify.Epsilon < vals[j] {
									vals[j] = 1.0
						values[i] = rgbToToken(vals[0], vals[1], vals[2])
						break
					} else if fun == Hsl || fun == Hsla && args[0].TokenType == css.NumberToken && args[2].TokenType == css.PercentageToken && args[4].TokenType == css.PercentageToken {
						vals[0] /= 360.0
						_, vals[0] = math.Modf(vals[0])
						if vals[0] < 0.0 {
							vals[0] = 1.0 + vals[0]
						r, g, b := css.HSL2RGB(vals[0], vals[1], vals[2])
						values[i] = rgbToToken(r, g, b)
						break
				} else if len(vals) == 4 {
					args[6] = minifyNumberPercentage(args[6])
				if 3 <= len(vals) && (fun == Rgb || fun == Rgba) {
					// 0%, 20%, 40%, 60%, 80% and 100% can be represented exactly as, 51, 102, 153, 204, and 255 respectively
					removePercentage := true
					for j := 0; j < 3; j++ {
						if args[j*2].TokenType != css.PercentageToken || 2.0*minify.Epsilon <= math.Mod(vals[j]+minify.Epsilon, 0.2) {
							removePercentage = false
							break
					if removePercentage {
						for j := 0; j < 3; j++ {
							args[j*2].TokenType = css.NumberToken
							if vals[j] < minify.Epsilon {
								args[j*2].Data = zeroBytes
							} else if math.Abs(vals[j]-0.2) < minify.Epsilon {
								args[j*2].Data = []byte("51")
							} else if math.Abs(vals[j]-0.4) < minify.Epsilon {
								args[j*2].Data = []byte("102")
							} else if math.Abs(vals[j]-0.6) < minify.Epsilon {
								args[j*2].Data = []byte("153")
							} else if math.Abs(vals[j]-0.8) < minify.Epsilon {
								args[j*2].Data = []byte("204")
							} else if math.Abs(vals[j]-1.0) < minify.Epsilon {
								args[j*2].Data = []byte("255")
	return values
func (c *cssMinifier) minifyProperty(prop Hash, values []Token) []Token {
	// limit maximum to prevent slow recursions (e.g. for background's append)
	if 100 < len(values) {
		return values
	switch prop {
	case Font:
		if len(values) > 1 { // must contain atleast font-size and font-family
			// the font-families are separated by commas and are at the end of font
			// get index for last token before font family names
			i := len(values) - 1
			for j, value := range values[2:] {
				if value.TokenType == css.CommaToken {
					i = 2 + j - 1 // identifier before first comma is a font-family
			// advance i while still at font-families when they contain spaces but no quotes
			for ; i > 0; i-- { // i cannot be 0, font-family must be prepended by font-size
				if values[i-1].TokenType == css.DelimToken && values[i-1].Data[0] == '/' {
				} else if values[i].TokenType != css.IdentToken && values[i].TokenType != css.StringToken {
				} else if h := values[i].Ident; h == Xx_Small || h == X_Small || h == Small || h == Medium || h == Large || h == X_Large || h == Xx_Large || h == Smaller || h == Larger || h == Inherit || h == Initial || h == Unset {
					// inherit, initial and unset are followed by an IdentToken/StringToken, so must be for font-size
			// font-family minified in place
			values = append(values[:i+1], c.minifyProperty(Font_Family, values[i+1:])...)
			// fix for IE9, IE10, IE11: font name starting with `-` is not recognized
			if values[i+1].Data[0] == '-' {
				v := make([]byte, len(values[i+1].Data)+2)
				v[0] = '\''
				copy(v[1:], values[i+1].Data)
				v[len(v)-1] = '\''
				values[i+1].Data = v
			if i > 0 {
				// line-height
				if i > 1 && values[i-1].TokenType == css.DelimToken && values[i-1].Data[0] == '/' {
					if values[i].Ident == Normal {
						values = append(values[:i-1], values[i+1:]...)
					i -= 2
				// font-size
				for ; i > -1; i-- {
					if values[i].Ident == Normal {
						values = append(values[:i], values[i+1:]...)
					} else if values[i].Ident == Bold {
						values[i].TokenType = css.NumberToken
						values[i].Data = n700Bytes
					} else if values[i].TokenType == css.NumberToken && bytes.Equal(values[i].Data, n400Bytes) {
						values = append(values[:i], values[i+1:]...)
	case Font_Family:
		for i, value := range values {
			if value.TokenType == css.StringToken && 2 < len(value.Data) {
				unquote := true
				parse.ToLower(value.Data)
				s := value.Data[1 : len(value.Data)-1]
				if 0 < len(s) {
					for _, split := range bytes.Split(s, spaceBytes) {
						// if len is zero, it contains two consecutive spaces
						if len(split) == 0 || !css.IsIdent(split) {
							unquote = false
							break
				if unquote {
					values[i].Data = s
	case Font_Weight:
		if values[0].Ident == Normal {
			values[0].TokenType = css.NumberToken
			values[0].Data = n400Bytes
		} else if values[0].Ident == Bold {
			values[0].TokenType = css.NumberToken
			values[0].Data = n700Bytes
		for i := 0; i < len(values); i++ {
			if values[i].TokenType == css.FunctionToken && len(values[i].Args) == 1 {
				fun := values[i].Fun
				data := values[i].Args[0].Data
				if fun == Local && (data[0] == '\'' || data[0] == '"') {
					if css.IsURLUnquoted(data[1 : len(data)-1]) {
						data = data[1 : len(data)-1]
					values[i].Args[0].Data = data
	case Margin, Padding, Border_Width:
		switch len(values) {
			if values[0].Equal(values[1]) {
				values = values[:1]
			if values[0].Equal(values[1]) && values[0].Equal(values[2]) {
				values = values[:1]
			} else if values[0].Equal(values[2]) {
				values = values[:2]
			if values[0].Equal(values[1]) && values[0].Equal(values[2]) && values[0].Equal(values[3]) {
				values = values[:1]
			} else if values[0].Equal(values[2]) && values[1].Equal(values[3]) {
				values = values[:2]
			} else if values[1].Equal(values[3]) {
				values = values[:3]
	case Border, Border_Bottom, Border_Left, Border_Right, Border_Top:
		for i := 0; i < len(values); i++ {
			if values[i].Ident == None || values[i].Ident == Currentcolor || values[i].Ident == Medium {
				values = append(values[:i], values[i+1:]...)
			} else {
				values[i] = minifyColor(values[i])
		if len(values) == 0 {
			values = []Token{{css.IdentToken, noneBytes, nil, 0, None}}
	case Outline:
		for i := 0; i < len(values); i++ {
			if values[i].Ident == Invert || values[i].Ident == None || values[i].Ident == Medium {
				values = append(values[:i], values[i+1:]...)
			} else {
				values[i] = minifyColor(values[i])
		if len(values) == 0 {
			values = []Token{{css.IdentToken, noneBytes, nil, 0, None}}
	case Background:
		start := 0
		for end := 0; end <= len(values); end++ { // loop over comma-separated lists
			if end != len(values) && values[end].TokenType != css.CommaToken {
				continue
			} else if start == end {
				start++
				continue
			// minify background-size and lowercase all identifiers
			for i := start; i < end; i++ {
				if values[i].TokenType == css.DelimToken && values[i].Data[0] == '/' {
					// background-size consists of either [<length-percentage> | auto | cover | contain] or [<length-percentage> | auto]{2}
					// we can only minify the latter
					if i+1 < end && (values[i+1].TokenType == css.NumberToken || values[i+1].IsLengthPercentage() || values[i+1].Ident == Auto) {
						if i+2 < end && (values[i+2].TokenType == css.NumberToken || values[i+2].IsLengthPercentage() || values[i+2].Ident == Auto) {
							sizeValues := c.minifyProperty(Background_Size, values[i+1:i+3])
							if len(sizeValues) == 1 && sizeValues[0].Ident == Auto {
								// remove background-size if it is '/ auto' after minifying the property
								values = append(values[:i], values[i+3:]...)
								end -= 3
								i--
							} else {
								values = append(values[:i+1], append(sizeValues, values[i+3:]...)...)
								end -= 2 - len(sizeValues)
								i += len(sizeValues) - 1
						} else if values[i+1].Ident == Auto {
							// remove background-size if it is '/ auto'
							values = append(values[:i], values[i+2:]...)
							end -= 2
			// minify all other values
			iPaddingBox := -1 // position of background-origin that is padding-box
			for i := start; i < end; i++ {
				h := values[i].Ident
				values[i] = minifyColor(values[i])
				if values[i].TokenType == css.IdentToken {
					if i+1 < end && values[i+1].TokenType == css.IdentToken && (h == Space || h == Round || h == Repeat || h == No_Repeat) {
						if h2 := values[i+1].Ident; h2 == Space || h2 == Round || h2 == Repeat || h2 == No_Repeat {
							repeatValues := c.minifyProperty(Background_Repeat, values[i:i+2])
							if len(repeatValues) == 1 && repeatValues[0].Ident == Repeat {
								values = append(values[:i], values[i+2:]...)
								end -= 2
								i--
							} else {
								values = append(values[:i], append(repeatValues, values[i+2:]...)...)
								end -= 2 - len(repeatValues)
								i += len(repeatValues) - 1
							continue
					} else if h == None || h == Scroll || h == Transparent {
						values = append(values[:i], values[i+1:]...)
						end--
						continue
					} else if h == Border_Box || h == Padding_Box {
						if iPaddingBox == -1 && h == Padding_Box { // background-origin
							iPaddingBox = i
						} else if iPaddingBox != -1 && h == Border_Box { // background-clip
							values = append(values[:i], values[i+1:]...)
							values = append(values[:iPaddingBox], values[iPaddingBox+1:]...)
							end -= 2
							i -= 2
						continue
				} else if values[i].TokenType == css.HashToken && bytes.Equal(values[i].Data, blackBytes) {
					values = append(values[:i], values[i+1:]...)
					continue
				// further minify background-position and background-size combination
				if values[i].TokenType == css.NumberToken || values[i].IsLengthPercentage() || h == Left || h == Right || h == Top || h == Bottom || h == Center {
					j := i + 1
					for ; j < len(values); j++ {
						if h := values[j].Ident; h == Left || h == Right || h == Top || h == Bottom || h == Center {
							continue
						} else if values[j].TokenType == css.NumberToken || values[j].IsLengthPercentage() {
							continue
						break
					positionValues := c.minifyProperty(Background_Position, values[i:j])
					hasSize := j < len(values) && values[j].TokenType == css.DelimToken && values[j].Data[0] == '/'
					if !hasSize && len(positionValues) == 2 && positionValues[0].IsZero() && positionValues[1].IsZero() {
						if end-start == 2 {
							values[i] = Token{css.NumberToken, zeroBytes, nil, 0, 0}
							values[i+1] = Token{css.NumberToken, zeroBytes, nil, 0, 0}
						} else {
							values = append(values[:i], values[j:]...)
							end -= j - i
					} else {
						if len(positionValues) == j-i {
							for k, positionValue := range positionValues {
								values[i+k] = positionValue
						} else {
							values = append(values[:i], append(positionValues, values[j:]...)...)
							end -= j - i - len(positionValues)
						i += len(positionValues) - 1
			if end-start == 0 {
				values = append(values[:start], append([]Token{{css.NumberToken, zeroBytes, nil, 0, 0}, {css.NumberToken, zeroBytes, nil, 0, 0}}, values[end:]...)...)
				end += 2
			start = end + 1
	case Background_Size:
		start := 0
		for end := 0; end <= len(values); end++ { // loop over comma-separated lists
			if end != len(values) && values[end].TokenType != css.CommaToken {
				continue
			} else if start == end {
				start++
				continue
			if end-start == 2 && values[start+1].Ident == Auto {
				values = append(values[:start+1], values[start+2:]...)
			start = end + 1
	case Background_Repeat:
		start := 0
		for end := 0; end <= len(values); end++ { // loop over comma-separated lists
			if end != len(values) && values[end].TokenType != css.CommaToken {
				continue
			} else if start == end {
				start++
				continue
			if end-start == 2 && values[start].TokenType == css.IdentToken && values[start+1].TokenType == css.IdentToken {
				if values[start].Ident == values[start+1].Ident {
					values = append(values[:start+1], values[start+2:]...)
				} else if values[start].Ident == Repeat && values[start+1].Ident == No_Repeat {
					values[start].Data = repeatXBytes
					values[start].Ident = Repeat_X
					values = append(values[:start+1], values[start+2:]...)
				} else if values[start].Ident == No_Repeat && values[start+1].Ident == Repeat {
					values[start].Data = repeatYBytes
					values[start].Ident = Repeat_Y
					values = append(values[:start+1], values[start+2:]...)
			start = end + 1
	case Background_Position:
		start := 0
		for end := 0; end <= len(values); end++ { // loop over comma-separated lists
			if end != len(values) && values[end].TokenType != css.CommaToken {
				continue
			} else if start == end {
				start++
				continue
			if end-start == 3 || end-start == 4 {
				// remove zero offsets
				for _, i := range []int{end - start - 1, start + 1} {
					if 2 < end-start && values[i].IsZero() {
						values = append(values[:i], values[i+1:]...)
						end--
				j := start + 1 // position of second set of horizontal/vertical values
				if 2 < end-start && values[start+2].TokenType == css.IdentToken {
					j = start + 2
				b := make([]byte, 0, 4)
				offsets := make([]Token, 2)
				for _, i := range []int{j, start} {
					if i+1 < end && i+1 != j {
						if values[i+1].TokenType == css.PercentageToken {
							// change right or bottom with percentage offset to left or top respectively
							if values[i].Ident == Right || values[i].Ident == Bottom {
								n, _ := strconvParse.ParseInt(values[i+1].Data[:len(values[i+1].Data)-1])
								b = strconv.AppendInt(b[:0], 100-n, 10)
								b = append(b, '%')
								values[i+1].Data = b
								if values[i].Ident == Right {
									values[i].Data = leftBytes
									values[i].Ident = Left
								} else {
									values[i].Data = topBytes
									values[i].Ident = Top
						if values[i].Ident == Left {
							offsets[0] = values[i+1]
						} else if values[i].Ident == Top {
							offsets[1] = values[i+1]
					} else if values[i].Ident == Left {
						offsets[0] = Token{css.NumberToken, zeroBytes, nil, 0, 0}
					} else if values[i].Ident == Top {
						offsets[1] = Token{css.NumberToken, zeroBytes, nil, 0, 0}
					} else if values[i].Ident == Right {
						offsets[0] = Token{css.PercentageToken, n100pBytes, nil, 0, 0}
						values[i].Ident = Left
					} else if values[i].Ident == Bottom {
						offsets[1] = Token{css.PercentageToken, n100pBytes, nil, 0, 0}
						values[i].Ident = Top
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