diff --git a/lib/Epub/Epub/blocks/BlockStyle.h b/lib/Epub/Epub/blocks/BlockStyle.h
index 63b054c9..a5a616bf 100644
--- a/lib/Epub/Epub/blocks/BlockStyle.h
+++ b/lib/Epub/Epub/blocks/BlockStyle.h
@@ -64,21 +64,27 @@ struct BlockStyle {
   // Create a BlockStyle from CSS style properties, resolving CssLength values to pixels
   // emSize is the current font line height, used for em/rem unit conversion
   // paragraphAlignment is the user's paragraphAlignment setting preference
-  static BlockStyle fromCssStyle(const CssStyle& cssStyle, const float emSize, const CssTextAlign paragraphAlignment) {
+  static BlockStyle fromCssStyle(const CssStyle& cssStyle, const float emSize, const CssTextAlign paragraphAlignment,
+                                 const uint16_t viewportWidth = 0) {
     BlockStyle blockStyle;
-    // Resolve all CssLength values to pixels using the current font's em size
-    blockStyle.marginTop = cssStyle.marginTop.toPixelsInt16(emSize);
-    blockStyle.marginBottom = cssStyle.marginBottom.toPixelsInt16(emSize);
-    blockStyle.marginLeft = cssStyle.marginLeft.toPixelsInt16(emSize);
-    blockStyle.marginRight = cssStyle.marginRight.toPixelsInt16(emSize);
+    const float vw = viewportWidth;
+    // Resolve all CssLength values to pixels using the current font's em size and viewport width
+    blockStyle.marginTop = cssStyle.marginTop.toPixelsInt16(emSize, vw);
+    blockStyle.marginBottom = cssStyle.marginBottom.toPixelsInt16(emSize, vw);
+    blockStyle.marginLeft = cssStyle.marginLeft.toPixelsInt16(emSize, vw);
+    blockStyle.marginRight = cssStyle.marginRight.toPixelsInt16(emSize, vw);
 
-    blockStyle.paddingTop = cssStyle.paddingTop.toPixelsInt16(emSize);
-    blockStyle.paddingBottom = cssStyle.paddingBottom.toPixelsInt16(emSize);
-    blockStyle.paddingLeft = cssStyle.paddingLeft.toPixelsInt16(emSize);
-    blockStyle.paddingRight = cssStyle.paddingRight.toPixelsInt16(emSize);
+    blockStyle.paddingTop = cssStyle.paddingTop.toPixelsInt16(emSize, vw);
+    blockStyle.paddingBottom = cssStyle.paddingBottom.toPixelsInt16(emSize, vw);
+    blockStyle.paddingLeft = cssStyle.paddingLeft.toPixelsInt16(emSize, vw);
+    blockStyle.paddingRight = cssStyle.paddingRight.toPixelsInt16(emSize, vw);
 
-    blockStyle.textIndent = cssStyle.textIndent.toPixelsInt16(emSize);
-    blockStyle.textIndentDefined = cssStyle.hasTextIndent();
+    // For textIndent: if it's a percentage we can't resolve (no viewport width),
+    // leave textIndentDefined=false so the EmSpace fallback in applyParagraphIndent() is used
+    if (cssStyle.hasTextIndent() && cssStyle.textIndent.isResolvable(vw)) {
+      blockStyle.textIndent = cssStyle.textIndent.toPixelsInt16(emSize, vw);
+      blockStyle.textIndentDefined = true;
+    }
     blockStyle.textAlignDefined = cssStyle.hasTextAlign();
     // User setting overrides CSS, unless "Book's Style" alignment setting is selected
     if (paragraphAlignment == CssTextAlign::None) {
diff --git a/lib/Epub/Epub/css/CssParser.cpp b/lib/Epub/Epub/css/CssParser.cpp
index d51ebba7..ba187e4c 100644
--- a/lib/Epub/Epub/css/CssParser.cpp
+++ b/lib/Epub/Epub/css/CssParser.cpp
@@ -283,6 +283,8 @@ CssLength CssParser::interpretLength(const std::string& val) {
     unit = CssUnit::Rem;
   } else if (unitPart == "pt") {
     unit = CssUnit::Points;
+  } else if (unitPart == "%") {
+    unit = CssUnit::Percent;
   }
   // px and unitless default to Pixels
 
@@ -518,7 +520,7 @@ CssStyle CssParser::parseInlineStyle(const std::string& styleValue) { return par
 // Cache serialization
 
 // Cache format version - increment when format changes
-constexpr uint8_t CSS_CACHE_VERSION = 1;
+constexpr uint8_t CSS_CACHE_VERSION = 2;
 
 bool CssParser::saveToCache(FsFile& file) const {
   if (!file) {
diff --git a/lib/Epub/Epub/css/CssStyle.h b/lib/Epub/Epub/css/CssStyle.h
index adbc19e2..b90fa7ab 100644
--- a/lib/Epub/Epub/css/CssStyle.h
+++ b/lib/Epub/Epub/css/CssStyle.h
@@ -4,7 +4,7 @@
 
 // Matches order of PARAGRAPH_ALIGNMENT in CrossPointSettings
 enum class CssTextAlign : uint8_t { Justify = 0, Left = 1, Center = 2, Right = 3, None = 4 };
-enum class CssUnit : uint8_t { Pixels = 0, Em = 1, Rem = 2, Points = 3 };
+enum class CssUnit : uint8_t { Pixels = 0, Em = 1, Rem = 2, Points = 3, Percent = 4 };
 
 // Represents a CSS length value with its unit, allowing deferred resolution to pixels
 struct CssLength {
@@ -17,21 +17,32 @@ struct CssLength {
   // Convenience constructor for pixel values (most common case)
   explicit CssLength(const float pixels) : value(pixels) {}
 
+  // Returns true if this length can be resolved to pixels with the given context.
+  // Percentage units require a non-zero containerWidth to resolve.
+  [[nodiscard]] bool isResolvable(const float containerWidth = 0) const {
+    return unit != CssUnit::Percent || containerWidth > 0;
+  }
+
   // Resolve to pixels given the current em size (font line height)
-  [[nodiscard]] float toPixels(const float emSize) const {
+  // containerWidth is needed for percentage units (e.g. viewport width)
+  [[nodiscard]] float toPixels(const float emSize, const float containerWidth = 0) const {
     switch (unit) {
       case CssUnit::Em:
       case CssUnit::Rem:
         return value * emSize;
       case CssUnit::Points:
         return value * 1.33f;  // Approximate pt to px conversion
+      case CssUnit::Percent:
+        return value * containerWidth / 100.0f;
       default:
         return value;
     }
   }
 
   // Resolve to int16_t pixels (for BlockStyle fields)
-  [[nodiscard]] int16_t toPixelsInt16(const float emSize) const { return static_cast<int16_t>(toPixels(emSize)); }
+  [[nodiscard]] int16_t toPixelsInt16(const float emSize, const float containerWidth = 0) const {
+    return static_cast<int16_t>(toPixels(emSize, containerWidth));
+  }
 };
 
 // Font style options matching CSS font-style property
diff --git a/lib/Epub/Epub/parsers/ChapterHtmlSlimParser.cpp b/lib/Epub/Epub/parsers/ChapterHtmlSlimParser.cpp
index 043cfca7..a4d10832 100644
--- a/lib/Epub/Epub/parsers/ChapterHtmlSlimParser.cpp
+++ b/lib/Epub/Epub/parsers/ChapterHtmlSlimParser.cpp
@@ -213,12 +213,12 @@ void XMLCALL ChapterHtmlSlimParser::startElement(void* userData, const XML_Char*
   }
 
   const float emSize = static_cast<float>(self->renderer.getLineHeight(self->fontId)) * self->lineCompression;
-  const auto userAlignmentBlockStyle =
-      BlockStyle::fromCssStyle(cssStyle, emSize, static_cast<CssTextAlign>(self->paragraphAlignment));
+  const auto userAlignmentBlockStyle = BlockStyle::fromCssStyle(
+      cssStyle, emSize, static_cast<CssTextAlign>(self->paragraphAlignment), self->viewportWidth);
 
   if (matches(name, HEADER_TAGS, NUM_HEADER_TAGS)) {
     self->currentCssStyle = cssStyle;
-    auto headerBlockStyle = BlockStyle::fromCssStyle(cssStyle, emSize, CssTextAlign::Center);
+    auto headerBlockStyle = BlockStyle::fromCssStyle(cssStyle, emSize, CssTextAlign::Center, self->viewportWidth);
     headerBlockStyle.textAlignDefined = true;
     if (self->embeddedStyle && cssStyle.hasTextAlign()) {
       headerBlockStyle.alignment = cssStyle.textAlign;