Setting "all : keyword" in iBooks

all_iBooks.css

/*  Testing initial and unset in iBooks
    All those styles are applied.
    Comments in .unset if different value */

/* all : initial */

.initial {
  -webkit-animation-delay: 0s;
  -webkit-animation-direction: normal;
  -webkit-animation-duration: 0s;
  -webkit-animation-fill-mode: none;
  -webkit-animation-iteration-count: 1;
  -webkit-animation-name: none;
  -webkit-animation-play-state: running;
  -webkit-animation-timing-function: ease;
  -webkit-appearance: none;
  -webkit-backdrop-filter: none;
  -webkit-backface-visibility: visible;
  -webkit-background-clip: border-box;
  -webkit-background-composite: source-over;
  -webkit-background-origin: padding-box;
  -webkit-background-size: auto;
  -webkit-border-fit: border;
  -webkit-border-horizontal-spacing: 0px;
  -webkit-border-image: none;
  -webkit-border-vertical-spacing: 0px;
  -webkit-box-align: stretch;
  -webkit-box-decoration-break: slice;
  -webkit-box-direction: normal;
  -webkit-box-flex: 0;
  -webkit-box-flex-group: 1;
  -webkit-box-lines: single;
  -webkit-box-ordinal-group: 1;
  -webkit-box-orient: horizontal;
  -webkit-box-pack: start;
  -webkit-box-reflect: none;
  -webkit-box-shadow: none;
  -webkit-clip-path: none;
  -webkit-color-correction: default;
  -webkit-column-axis: auto;
  -webkit-column-break-after: auto;
  -webkit-column-break-before: auto;
  -webkit-column-break-inside: auto;
  -webkit-cursor-visibility: auto;
  -webkit-dashboard-region: ;
  -webkit-flow-from: none;
  -webkit-flow-into: none;
  -webkit-font-kerning: auto;
  -webkit-font-smoothing: auto;
  -webkit-hyphenate-character: auto;
  -webkit-hyphenate-limit-after: auto;
  -webkit-hyphenate-limit-before: auto;
  -webkit-hyphenate-limit-lines: no-limit;
  -webkit-hyphens: manual;
  -webkit-initial-letter: normal;
  -webkit-line-align: none;
  -webkit-line-box-contain: block inline replaced;
  -webkit-line-break: auto;
  -webkit-line-clamp: none;
  -webkit-line-grid: none;
  -webkit-line-snap: none;
  -webkit-locale: auto;
  -webkit-margin-after-collapse: collapse;
  -webkit-margin-before-collapse: collapse;
  -webkit-marquee-direction: auto;
  -webkit-marquee-increment: 6px;
  -webkit-marquee-repetition: infinite;
  -webkit-marquee-style: scroll;
  -webkit-mask-box-image: none;
  -webkit-mask-box-image-outset: 0px;
  -webkit-mask-box-image-repeat: stretch;
  -webkit-mask-box-image-slice: 0;
  -webkit-mask-box-image-source: none;
  -webkit-mask-box-image-width: auto;
  -webkit-mask-clip: border-box;
  -webkit-mask-composite: source-over;
  -webkit-mask-image: none;
  -webkit-mask-origin: border-box;
  -webkit-mask-size: auto;
  -webkit-mask-source-type: alpha;
  -webkit-nbsp-mode: normal;
  -webkit-print-color-adjust: economy;
  -webkit-region-break-after: auto;
  -webkit-region-break-before: auto;
  -webkit-region-break-inside: auto;
  -webkit-region-fragment: auto;
  -webkit-rtl-ordering: logical;
  -webkit-scroll-snap-coordinate: none;
  -webkit-scroll-snap-destination: 0px 0px;
  -webkit-scroll-snap-points-x: none;
  -webkit-scroll-snap-points-y: none;
  -webkit-scroll-snap-type: none;
  -webkit-shape-image-threshold: 0;
  -webkit-shape-margin: 0px;
  -webkit-shape-outside: none;
  -webkit-svg-shadow: none;
  -webkit-text-combine: none;
  -webkit-text-decoration-color: rgb(0, 0, 0);
  -webkit-text-decoration-line: none;
  -webkit-text-decoration-skip: auto;
  -webkit-text-decoration-style: solid;
  -webkit-text-decorations-in-effect: none;
  -webkit-text-emphasis-color: rgb(0, 0, 0);
  -webkit-text-emphasis-position: over right;
  -webkit-text-emphasis-style: none;
  -webkit-text-fill-color: rgb(0, 0, 0);
  -webkit-text-orientation: vertical-right;
  -webkit-text-security: none;
  -webkit-text-stroke-color: rgb(0, 0, 0);
  -webkit-text-stroke-width: 0px;
  -webkit-text-underline-position: auto;
  -webkit-transform-style: flat;
  -webkit-transition-delay: 0s;
  -webkit-transition-duration: 0s;
  -webkit-transition-property: all;
  -webkit-transition-timing-function: ease;
  -webkit-user-drag: auto;
  -webkit-user-modify: read-only;
  -webkit-user-select: text;
  -webkit-writing-mode: horizontal-tb;
  align-content: start;
  align-items: start;
  align-self: start;
  alignment-baseline: auto;
  alt: '';
  animation-delay: 0s;
  animation-direction: normal;
  animation-duration: 0s;
  animation-fill-mode: none;
  animation-iteration-count: 1;
  animation-name: none;
  animation-play-state: running;
  animation-timing-function: ease;
  background-attachment: scroll;
  background-blend-mode: normal;
  background-clip: border-box;
  background-color: rgba(0, 0, 0, 0);
  background-image: none;
  background-origin: padding-box;
  background-size: auto;
  baseline-shift: baseline;
  border-bottom-color: rgb(0, 0, 0);
  border-bottom-left-radius: 0px;
  border-bottom-right-radius: 0px;
  border-bottom-style: none;
  border-bottom-width: 0px;
  border-collapse: separate;
  border-image-outset: 0px;
  border-image-repeat: stretch;
  border-image-slice: 100%;
  border-image-source: none;
  border-image-width: 1;
  border-left-color: rgb(0, 0, 0);
  border-left-style: none;
  border-left-width: 0px;
  border-right-color: rgb(0, 0, 0);
  border-right-style: none;
  border-right-width: 0px;
  border-top-color: rgb(0, 0, 0);
  border-top-left-radius: 0px;
  border-top-right-radius: 0px;
  border-top-style: none;
  border-top-width: 0px;
  bottom: auto;
  box-shadow: none;
  box-sizing: content-box;
  buffered-rendering: auto;
  caption-side: top;
  clear: none;
  clip: auto;
  clip-path: none;
  clip-rule: nonzero;
  color: rgb(0, 0, 0);
  color-interpolation: srgb;
  color-interpolation-filters: linearrgb;
  color-rendering: auto;
  column-count: auto;
  column-fill: balance;
  column-gap: normal;
  column-progression: normal;
  column-rule-color: rgb(0, 0, 0);
  column-rule-style: none;
  column-rule-width: 0px;
  column-span: none;
  column-width: auto;
  cursor: auto;
  cx: 0px;
  cy: 0px;
  display: inline;
  dominant-baseline: auto;
  empty-cells: show;
  fill: #000000;
  fill-opacity: 1;
  fill-rule: nonzero;
  filter: none;
  flex-basis: auto;
  flex-direction: row;
  flex-grow: 0;
  flex-shrink: 1;
  flex-wrap: nowrap;
  float: none;
  flood-color: rgb(0, 0, 0);
  flood-opacity: 1;
  font-family: iBooks_Times_New_Roman;
  font-size: 15px;
  font-style: normal;
  font-synthesis: style weight;
  font-variant-alternates: normal;
  font-variant-caps: normal;
  font-variant-east-asian: normal;
  font-variant-ligatures: normal;
  font-variant-numeric: normal;
  font-variant-position: normal;
  font-weight: normal;
  glyph-orientation-horizontal: 0deg;
  glyph-orientation-vertical: auto;
  height: auto;
  image-rendering: auto;
  isolation: auto;
  justify-content: start;
  justify-items: start;
  justify-self: start;
  kerning: 0;
  left: auto;
  letter-spacing: normal;
  lighting-color: rgb(255, 255, 255);
  line-height: 17px;
  list-style-image: none;
  list-style-position: outside;
  list-style-type: disc;
  margin-bottom: 0px;
  margin-left: 0px;
  margin-right: 0px;
  margin-top: 0px;
  marker-end: none;
  marker-mid: none;
  marker-start: none;
  mask: none;
  mask-type: luminance;
  max-height: none;
  max-width: none;
  min-height: 0px;
  min-width: 0px;
  mix-blend-mode: normal;
  opacity: 1;
  order: 0;
  orphans: auto;
  outline-color: rgb(0, 0, 0);
  outline-offset: 0px;
  outline-style: none;
  outline-width: 0px;
  overflow-wrap: normal;
  overflow-x: visible;
  overflow-y: visible;
  padding-bottom: 0px;
  padding-left: 0px;
  padding-right: 0px;
  padding-top: 0px;
  page-break-after: auto;
  page-break-before: auto;
  page-break-inside: auto;
  paint-order: normal;
  perspective: none;
  pointer-events: auto;
  position: static;
  r: 0px;
  resize: none;
  right: auto;
  rx: 0px;
  ry: 0px;
  shape-rendering: auto;
  speak: normal;
  stop-color: rgb(0, 0, 0);
  stop-opacity: 1;
  stroke: none;
  stroke-dasharray: none;
  stroke-dashoffset: 0px;
  stroke-linecap: butt;
  stroke-linejoin: miter;
  stroke-miterlimit: 4;
  stroke-opacity: 1;
  stroke-width: 1px;
  tab-size: 8;
  table-layout: auto;
  text-align: justify;
  text-anchor: start;
  text-decoration: none;
  text-indent: 0px;
  text-overflow: clip;
  text-rendering: auto;
  text-shadow: none;
  text-transform: none;
  top: auto;
  transform: none;
  transform-style: flat;
  transition-delay: 0s;
  transition-duration: 0s;
  transition-property: all;
  transition-timing-function: ease;
  vector-effect: none;
  vertical-align: baseline;
  visibility: visible;
  white-space: normal;
  widows: auto;
  width: auto;
  word-break: normal;
  word-spacing: 0px;
  word-wrap: normal;
  writing-mode: lr-tb;
  x: 0px;
  y: 0px;
  z-index: auto;
  zoom: 1;
}

/* all: unset */

.unset {
  -webkit-animation-delay: 0s;
  -webkit-animation-direction: normal;
  -webkit-animation-duration: 0s;
  -webkit-animation-fill-mode: none;
  -webkit-animation-iteration-count: 1;
  -webkit-animation-name: none;
  -webkit-animation-play-state: running;
  -webkit-animation-timing-function: ease;
  -webkit-appearance: none;
  -webkit-backdrop-filter: none;
  -webkit-backface-visibility: visible;
  -webkit-background-clip: border-box;
  -webkit-background-composite: source-over;
  -webkit-background-origin: padding-box;
  -webkit-background-size: auto;
  -webkit-border-fit: border;
  -webkit-border-horizontal-spacing: 0px;
  -webkit-border-image: none;
  -webkit-border-vertical-spacing: 0px;
  -webkit-box-align: stretch;
  -webkit-box-decoration-break: slice;
  -webkit-box-direction: normal;
  -webkit-box-flex: 0;
  -webkit-box-flex-group: 1;
  -webkit-box-lines: single;
  -webkit-box-ordinal-group: 1;
  -webkit-box-orient: horizontal;
  -webkit-box-pack: start;
  -webkit-box-reflect: none;
  -webkit-box-shadow: none;
  -webkit-clip-path: none;
  -webkit-color-correction: default;
  -webkit-column-axis: auto;
  -webkit-column-break-after: auto;
  -webkit-column-break-before: auto;
  -webkit-column-break-inside: auto;
  -webkit-cursor-visibility: auto;
  -webkit-dashboard-region: ;
  -webkit-flow-from: none;
  -webkit-flow-into: none;
  -webkit-font-kerning: auto;
  -webkit-font-smoothing: subpixel-antialiased;     /* Different */
  -webkit-hyphenate-character: '-';                 /* Different */
  -webkit-hyphenate-limit-after: 2;                 /* Different */
  -webkit-hyphenate-limit-before: 2;                /* Different */
  -webkit-hyphenate-limit-lines: 3;                 /* Different */
  -webkit-hyphens: auto;                            /* Different */
  -webkit-initial-letter: normal;
  -webkit-line-align: none;
  -webkit-line-box-contain: block glyphs replaced;  /* Different */
  -webkit-line-break: auto;
  -webkit-line-clamp: none;
  -webkit-line-grid: none;
  -webkit-line-snap: none;
  -webkit-locale: fr;                               /* Different */
  -webkit-margin-after-collapse: collapse;
  -webkit-margin-before-collapse: collapse;
  -webkit-marquee-direction: auto;
  -webkit-marquee-increment: 6px;
  -webkit-marquee-repetition: infinite;
  -webkit-marquee-style: scroll;
  -webkit-mask-box-image: none;
  -webkit-mask-box-image-outset: 0px;
  -webkit-mask-box-image-repeat: stretch;
  -webkit-mask-box-image-slice: 0;
  -webkit-mask-box-image-source: none;
  -webkit-mask-box-image-width: auto;
  -webkit-mask-clip: border-box;
  -webkit-mask-composite: source-over;
  -webkit-mask-image: none;
  -webkit-mask-origin: border-box;
  -webkit-mask-size: auto;
  -webkit-mask-source-type: alpha;
  -webkit-nbsp-mode: normal;
  -webkit-print-color-adjust: economy;
  -webkit-region-break-after: auto;
  -webkit-region-break-before: auto;
  -webkit-region-break-inside: auto;
  -webkit-region-fragment: auto;
  -webkit-rtl-ordering: logical;
  -webkit-scroll-snap-coordinate: none;
  -webkit-scroll-snap-destination: 0px 0px;
  -webkit-scroll-snap-points-x: none;
  -webkit-scroll-snap-points-y: none;
  -webkit-scroll-snap-type: none;
  -webkit-shape-image-threshold: 0;
  -webkit-shape-margin: 0px;
  -webkit-shape-outside: none;
  -webkit-svg-shadow: none;
  -webkit-text-combine: none;
  -webkit-text-decoration-color: rgb(36, 36, 36);   /* Different */
  -webkit-text-decoration-line: none;
  -webkit-text-decoration-skip: auto;
  -webkit-text-decoration-style: solid;
  -webkit-text-decorations-in-effect: none;
  -webkit-text-emphasis-color: rgb(36, 36, 36);     /* Different */
  -webkit-text-emphasis-position: over right;
  -webkit-text-emphasis-style: none;
  -webkit-text-fill-color: rgb(36, 36, 36);         /* Different */
  -webkit-text-orientation: vertical-right;
  -webkit-text-security: none;
  -webkit-text-stroke-color: rgb(36, 36, 36);       /* Different */
  -webkit-text-stroke-width: 0px;
  -webkit-text-underline-position: auto;
  -webkit-transform-style: flat;
  -webkit-transition-delay: 0s;
  -webkit-transition-duration: 0s;
  -webkit-transition-property: all;
  -webkit-transition-timing-function: ease;
  -webkit-user-drag: auto;
  -webkit-user-modify: read-only;
  -webkit-user-select: text;
  -webkit-writing-mode: horizontal-tb;
  align-content: start;
  align-items: start;
  align-self: start;
  alignment-baseline: auto;
  alt: '';
  animation-delay: 0s;
  animation-direction: normal;
  animation-duration: 0s;
  animation-fill-mode: none;
  animation-iteration-count: 1;
  animation-name: none;
  animation-play-state: running;
  animation-timing-function: ease;
  background-attachment: scroll;
  background-blend-mode: normal;
  background-clip: border-box;
  background-color: rgba(0, 0, 0, 0);
  background-image: none;
  background-origin: padding-box;
  background-size: auto;
  baseline-shift: baseline;
  border-bottom-color: rgb(36, 36, 36);           /* Different */
  border-bottom-left-radius: 0px;
  border-bottom-right-radius: 0px;
  border-bottom-style: none;
  border-bottom-width: 0px;
  border-collapse: separate;
  border-image-outset: 0px;
  border-image-repeat: stretch;
  border-image-slice: 100%;
  border-image-source: none;
  border-image-width: 1;
  border-left-color: rgb(36, 36, 36);             /* Different */
  border-left-style: none;
  border-left-width: 0px;
  border-right-color: rgb(36, 36, 36);            /* Different */
  border-right-style: none;
  border-right-width: 0px;
  border-top-color: rgb(36, 36, 36);              /* Different */
  border-top-left-radius: 0px;
  border-top-right-radius: 0px;
  border-top-style: none;
  border-top-width: 0px;
  bottom: auto;
  box-shadow: none;
  box-sizing: content-box;
  buffered-rendering: auto;
  caption-side: top;
  clear: none;
  clip: auto;
  clip-path: none;
  clip-rule: nonzero;
  color: rgb(36, 36, 36);                         /* Different */
  color-interpolation: srgb;
  color-interpolation-filters: linearrgb;
  color-rendering: auto;
  column-count: auto;
  column-fill: balance;
  column-gap: normal;
  column-progression: normal;
  column-rule-color: rgb(36, 36, 36);             /* Different */
  column-rule-style: none;
  column-rule-width: 0px;
  column-span: none;
  column-width: auto;
  cursor: auto;
  cx: 0px;
  cy: 0px;
  display: inline;
  dominant-baseline: auto;
  empty-cells: show;
  fill: #000000;
  fill-opacity: 1;
  fill-rule: nonzero;
  filter: none;
  flex-basis: auto;
  flex-direction: row;
  flex-grow: 0;
  flex-shrink: 1;
  flex-wrap: nowrap;
  float: none;
  flood-color: rgb(0, 0, 0);
  flood-opacity: 1;
  font-family: {font-used};                 /* Different */
  font-size: {current-size};                /* Different */
  font-style: normal;
  font-synthesis: style weight;
  font-variant-alternates: normal;
  font-variant-caps: normal;
  font-variant-east-asian: normal;
  font-variant-ligatures: normal;
  font-variant-numeric: normal;
  font-variant-position: normal;
  font-weight: normal;
  glyph-orientation-horizontal: 0deg;
  glyph-orientation-vertical: auto;
  height: auto;
  image-rendering: auto;
  isolation: auto;
  justify-content: start;
  justify-items: start;
  justify-self: start;
  kerning: 0;
  left: auto;
  letter-spacing: normal;
  lighting-color: rgb(255, 255, 255);
  line-height: {current-line-height};               /* Different */
  list-style-image: none;
  list-style-position: outside;
  list-style-type: disc;
  margin-bottom: 0px;
  margin-left: 0px;
  margin-right: 0px;
  margin-top: 0px;
  marker-end: none;
  marker-mid: none;
  marker-start: none;
  mask: none;
  mask-type: luminance;
  max-height: none;
  max-width: none;
  min-height: 0px;
  min-width: 0px;
  mix-blend-mode: normal;
  opacity: 1;
  order: 0;
  orphans: auto;
  outline-color: rgb(36, 36, 36);             /* Different */
  outline-offset: 0px;
  outline-style: none;
  outline-width: 0px;
  overflow-wrap: normal;
  overflow-x: visible;
  overflow-y: visible;
  padding-bottom: 0px;
  padding-left: 0px;
  padding-right: 0px;
  padding-top: 0px;
  page-break-after: auto;
  page-break-before: auto;
  page-break-inside: auto;
  paint-order: normal;
  perspective: none;
  pointer-events: auto;
  position: static;
  r: 0px;
  resize: none;
  right: auto;
  rx: 0px;
  ry: 0px;
  shape-rendering: auto;
  speak: normal;
  stop-color: rgb(0, 0, 0);
  stop-opacity: 1;
  stroke: none;
  stroke-dasharray: none;
  stroke-dashoffset: 0px;
  stroke-linecap: butt;
  stroke-linejoin: miter;
  stroke-miterlimit: 4;
  stroke-opacity: 1;
  stroke-width: 1px;
  tab-size: 8;
  table-layout: auto;
  text-align: start;                    /* Different */
  text-anchor: start;
  text-decoration: none;
  text-indent: 0px;
  text-overflow: clip;
  text-rendering: auto;
  text-shadow: none;
  text-transform: none;
  top: auto;
  transform: none;
  transform-style: flat;
  transition-delay: 0s;
  transition-duration: 0s;
  transition-property: all;
  transition-timing-function: ease;
  vector-effect: none;
  vertical-align: baseline;
  visibility: visible;
  white-space: normal;
  widows: auto;
  width: auto;
  word-break: normal;
  word-spacing: 0px;
  word-wrap: normal;
  writing-mode: lr-tb;
  x: 0px;
  y: 0px;
  z-index: auto;
  zoom: 1;
}

Interesting docs

Beware, the difference is somewhat hard to grasp.

Example: max-height. iBooks has a default override for img which is somehow applied even when you override it.

Initial

• MDN: https://developer.mozilla.org/en-US/docs/Web/CSS/initial_value
• CSS Spec: https://drafts.csswg.org/css-cascade-3/#initial-value

Each property has an initial value, defined in the property’s definition table. If the property is not an inherited property, and the cascade does not result in a value, then the specified value of the property is its initial value.

→ The cascade results in a value since max-height: 95% !important in iBooks’ default CSS.

Unset

• MDN: https://developer.mozilla.org/en-US/docs/Web/CSS/unset
• CSS Spec: https://drafts.csswg.org/css-cascade-3/#inherit-initial

If the cascaded value of a property is the unset keyword, then if it is an inherited property, this is treated as inherit, and if it is not, this is treated as initial. This keyword effectively erases all declared values occurring earlier in the cascade, correctly inheriting or not as appropriate for the property (or all longhands of a shorthand).

→ The value is inherited from max-height: 95% !important.