There are a number of differences between HtmlStyle and the stylesheet that should be investigated.

Some are expected and are OK; others may indicate unused items, particularly in the stylesheet.

Here is the output from a relatively simple program to compare the two. It does not (yet) take "known" or "expected" differences into account. (The program is attached.)

found 139 names in HtmlStyle
found 110 names in stylesheet
In HtmlStyle but not stylesheet: all-classes-index-page
In HtmlStyle but not stylesheet: all-packages-index-page
In HtmlStyle but not stylesheet: annotations
In HtmlStyle but not stylesheet: col-plain
In HtmlStyle but not stylesheet: constant-details
In HtmlStyle but not stylesheet: constants-summary
In HtmlStyle but not stylesheet: constants-summary-page
In HtmlStyle but not stylesheet: constructor-details
In HtmlStyle but not stylesheet: constructor-summary
In HtmlStyle but not stylesheet: deprecated-list-page
In HtmlStyle but not stylesheet: details-table
In HtmlStyle but not stylesheet: doc-file-page
In HtmlStyle but not stylesheet: element-name
In HtmlStyle but not stylesheet: extends-implements
In HtmlStyle but not stylesheet: external-link
In HtmlStyle but not stylesheet: field-details
In HtmlStyle but not stylesheet: field-summary
In HtmlStyle but not stylesheet: help-page
In HtmlStyle but not stylesheet: help-section
In HtmlStyle but not stylesheet: help-toc
In HtmlStyle but not stylesheet: hierarchy
In HtmlStyle but not stylesheet: index
In HtmlStyle but not stylesheet: index-page
In HtmlStyle but not stylesheet: index-redirect-page
In HtmlStyle but not stylesheet: member-details
In HtmlStyle but not stylesheet: member-summary
In HtmlStyle but not stylesheet: method-details
In HtmlStyle but not stylesheet: method-summary
In HtmlStyle but not stylesheet: modifiers
In HtmlStyle but not stylesheet: module-description
In HtmlStyle but not stylesheet: module-index-page
In HtmlStyle but not stylesheet: modules-summary
In HtmlStyle but not stylesheet: nested-class-summary
In HtmlStyle but not stylesheet: package-declaration-page
In HtmlStyle but not stylesheet: package-description
In HtmlStyle but not stylesheet: package-index-page
In HtmlStyle but not stylesheet: package-tree-page
In HtmlStyle but not stylesheet: package-use-page
In HtmlStyle but not stylesheet: package-uses
In HtmlStyle but not stylesheet: packages
In HtmlStyle but not stylesheet: packages-summary
In HtmlStyle but not stylesheet: permits
In HtmlStyle but not stylesheet: permits-note
In HtmlStyle but not stylesheet: preview-list-page
In HtmlStyle but not stylesheet: property-details
In HtmlStyle but not stylesheet: property-summary
In HtmlStyle but not stylesheet: return-type
In HtmlStyle but not stylesheet: serialized-form-page
In HtmlStyle but not stylesheet: serialized-package-container
In HtmlStyle but not stylesheet: services-summary
In HtmlStyle but not stylesheet: source-container
In HtmlStyle but not stylesheet: source-page
In HtmlStyle but not stylesheet: system-properties-page
In HtmlStyle but not stylesheet: tree-page
In stylesheet but not HtmlStyle: all-classes-container
In stylesheet but not HtmlStyle: all-packages-container
In stylesheet but not HtmlStyle: borderless
In stylesheet but not HtmlStyle: bottom-nav
In stylesheet but not HtmlStyle: clear
In stylesheet but not HtmlStyle: constant-values-container
In stylesheet but not HtmlStyle: css
In stylesheet but not HtmlStyle: deprecated-content
In stylesheet but not HtmlStyle: footer
In stylesheet but not HtmlStyle: hidden
In stylesheet but not HtmlStyle: module-graph
In stylesheet but not HtmlStyle: override-specify-label
In stylesheet but not HtmlStyle: plain
In stylesheet but not HtmlStyle: png
In stylesheet but not HtmlStyle: result-highlight
In stylesheet but not HtmlStyle: result-item
In stylesheet but not HtmlStyle: search-tag-desc-result
In stylesheet but not HtmlStyle: search-tag-holder-result
In stylesheet but not HtmlStyle: striped
In stylesheet but not HtmlStyle: tab
In stylesheet but not HtmlStyle: table-sub-heading-color
In stylesheet but not HtmlStyle: ui-autocomplete
In stylesheet but not HtmlStyle: ui-autocomplete-category
In stylesheet but not HtmlStyle: w3
In stylesheet but not HtmlStyle: watermark