Add CSS style inheritance to WithCustomCSS option

formatters/html/html.go

@@ -443,13 +443,37 @@ func (f *Formatter) styleToCSS(style *chroma.Style) map[chroma.TokenType]string
 		if t != chroma.Background {
 			entry = entry.Sub(bg)
 		}
-		if !f.allClasses && entry.IsZero() && f.customCSS[t] == `` {
+
+		// Inherit from custom CSS provided by user
+		tokenCategory := t.Category()
+		tokenSubCategory := t.SubCategory()
+		if t != tokenCategory {
+			if css, ok := f.customCSS[tokenCategory]; ok {
+				classes[t] = css
+			}
+		}
+		if tokenCategory != tokenSubCategory {
+			if css, ok := f.customCSS[tokenSubCategory]; ok {
+				classes[t] += css
+			}
+		}
+		// Add custom CSS provided by user
+		if css, ok := f.customCSS[t]; ok {
+			classes[t] += css
+		}
+
+		if !f.allClasses && entry.IsZero() && classes[t] == `` {
 			continue
 		}
-		classes[t] = f.customCSS[t] + StyleEntryToCSS(entry)
+
+		styleEntryCSS := StyleEntryToCSS(entry)
+		if styleEntryCSS != `` {
+			styleEntryCSS += `;`
+		}
+		classes[t] = styleEntryCSS + classes[t]
 	}
 	classes[chroma.Background] += f.tabWidthStyle()
-	classes[chroma.PreWrapper] += classes[chroma.Background] + `;`
+	classes[chroma.PreWrapper] += classes[chroma.Background]
 	// Make PreWrapper a grid to show highlight style with full width.
 	if len(f.highlightRanges) > 0 && f.customCSS[chroma.PreWrapper] == `` {
 		classes[chroma.PreWrapper] += `display: grid;`

formatters/html/html_test.go

@@ -120,6 +120,21 @@ func TestWithCustomCSS(t *testing.T) {
 	assert.Regexp(t, `<span style="display:flex;display:inline;"><span><span style=".*">echo</span> FOO</span></span>`, buf.String())
 }
 
+func TestWithCustomCSSStyleInheritance(t *testing.T) {
+	f := New(WithClasses(false), WithCustomCSS(map[chroma.TokenType]string{
+		chroma.String:              `background: blue;`,
+		chroma.LiteralStringDouble: `color: tomato;`,
+	}))
+	it, err := lexers.Get("bash").Tokenise(nil, `echo "FOO"`)
+	assert.NoError(t, err)
+
+	var buf bytes.Buffer
+	err = f.Format(&buf, styles.Fallback, it)
+	assert.NoError(t, err)
+
+	assert.Regexp(t, ` <span style=".*;background:blue;color:tomato;">&#34;FOO&#34;</span>`, buf.String())
+}
+
 func TestWrapLongLines(t *testing.T) {
 	f := New(WithClasses(false), WrapLongLines(true))
 	it, err := lexers.Get("go").Tokenise(nil, "package main\nfunc main()\n{\nprintln(\"hello world\")\n}\n")