@use "settings" as *;

// Paint the page's own background (page colour + the fixed 130deg gradient at
// 0.91, pre-composited with color-mix) so a sticky bar stays opaque to content
// scrolling under it while looking identical to the page behind it.
//
// styles.scss paints that backdrop as a real fixed layer: body::after is a
// `position: fixed` box at the viewport's top-left corner, viewport-wide and
// `height: 100vh` tall. Anything that has to disappear into it must show the
// slice of that box it covers. background-attachment: fixed asks the engine for
// exactly that, and iOS Safari does not honour it - it anchors the layer to the
// document instead, so the bar sweeps the whole ramp (cyan to purple over a
// long page) while the gutters beside it hold still. Chromium does honour it,
// which is why only a device caught this.
//
// So derive the alignment from geometry and ask for no feature at all. Each bar
// keeps a constant viewport offset - .header at the top, #diff-header directly
// below it - and both are flush with the viewport's right edge at every width:
// the action rail insets them from the *left* on a wide screen and widens again
// on hover, but nothing moves their right edge. Anchor a viewport-sized copy of
// the gradient to that edge and push it up by the bar's own offset, and the bar
// paints body::after's slice by construction, on any engine.
//
// $y-offset: the bar's distance from the top of the viewport.
@mixin page-surface-gradient($y-offset: 0px) {
  background: var(--color-background-gradient-second); // fallback, no color-mix
  // Longhands from here down, and no second `background:` shorthand after them -
  // one would silently reset size/position/origin back to their initial values.
  background-image: linear-gradient(130deg,
    color-mix(in srgb, var(--color-background-gradient-first) 91%, var(--color-background-page)),
    color-mix(in srgb, var(--color-background-gradient-second) 91%, var(--color-background-page)) 41.07%,
    color-mix(in srgb, var(--color-background-gradient-third) 91%, var(--color-background-page)) 84.05%);
  // 100vh to match body::after's own height: 100vh - same unit, so the two
  // resolve to the same number on iOS, where it means the large (toolbar
  // collapsed) viewport and therefore holds still as the toolbar moves.
  // 100vw for the width: the bars are as wide as the viewport only on a narrow
  // screen, so 100% would compress the ramp into the rail's leftovers on a
  // desktop one.
  background-size: 100vw 100vh;
  background-repeat: no-repeat;
  // border-box, or the bar's own padding would offset the copy by that much.
  background-origin: border-box;
  background-position: right 0 top calc(-1 * #{$y-offset});
}

#diff-form {

  background: rgba(0, 0, 0, .05);
  padding: 1em;
  border-radius: 10px;
  margin-bottom: 1em;
  color: #fff;
  font-size: 0.9rem;
  text-align: center;

  label.from-to-label {
    width: 4rem;
    text-decoration: none;
    padding: 0.5rem;

    &#change-from {
      color: #b30000;
      background: #fadad7
    }

    &#change-to {
      background: #eaf2c2;
      color: #406619;
    }
  }

  #diff-style {
    >span {
      display: inline-block;
      padding: 0.3em;
      label {
        font-weight: normal;
      }
    }
  }
  * {
    vertical-align: middle;
  }

}

body.difference-page {
  // Keep the top menu (watch URL, EDIT, theme/GitHub icons) on screen while the
  // diff scrolls, stacked above #diff-header. Scoped to the diff page on
  // purpose - upstream's @todo in parts/_top_menu.scss wants this globally, but
  // that is a separate change.
  //
  // Sticky makes .header a stacking context, so its mobile drawer / overlay
  // (z-index 10000 / 9999) are now capped by this value. 30 clears #diff-header
  // below and still leaves toasts (10000, fixed) painting over the bar.
  .header {
    position: sticky;
    top: 0;
    z-index: 30;
    @include page-surface-gradient(0px);
  }

  // The top line now carries the watch's name, so give it back the room the two
  // stacked left insets were taking. Its text starts $common-gap twice in: the
  // menu row's own padding, which every item on the row needs to clear the edge,
  // plus the link's own left margin, which on the row's first item only repeats
  // that padding. Drop the repeat and keep the row's padding: 8.8px back, and
  // the line still sits on the same left edge as the diff below it rather than
  // hard against the viewport. The right side of both is untouched - the link's
  // right margin still separates it from the menu icons.
  .current-diff-url {
    margin-left: 0;
  }

  // Wherever the hamburger is (max-width: $desktop-wide-breakpoint, set in
  // parts/_hamburger_menu.scss), the menu row is at its tightest and every item
  // on it competes with the watch name for the same line. The heart is the one
  // item on that row that is neither navigation nor status, so it is what gives
  // way - on this page only, and only under that width. Desktop diff pages and
  // every other page keep it.
  //
  // CSS rather than a {% if %} in base.html: the heart's own reason to exist is
  // that it is always there, and a template branch would take it off the page
  // entirely rather than fold it away with the rest of the row.
  @media only screen and (max-width: $desktop-wide-breakpoint) {
    #heart-us {
      display: none;
    }
  }

  // .app-main's 0.55rem gap sits between the two sticky bars, so #diff-header
  // starts 8.8px below the top menu and then slides up to meet it over the
  // first 8.8px of scroll - a visible twitch right as scrolling begins. The gap
  // can't be preserved once stuck (it is outside both bars, so the diff would
  // scroll through it), so close it here and let them sit flush at every scroll
  // position. Only the .header/section.content pair is affected; .app-main has
  // no other children.
  .app-main {
    gap: 0;
  }

  .tab-pane-inner {
    scroll-margin-top: calc(var(--app-header-height, 0px) + var(--diff-header-height, 0px) + 1rem);
  }

  // The 2px activity strip is fixed on body, so it lives in the root stacking
  // context and would paint over the mobile drawer now that the drawer is capped
  // inside .header's context above. Drop it below .header rather than raising
  // .header past the action rail (60), which would hide the rail's hover flyout.
  // Still above #diff-header (20) and the minimap (10); on this page it now also
  // passes under the rail's flyout, which is 2px of imperceptible overlap.
  #pure-menu-horizontal-spinner {
    z-index: 29;
  }

  // The thin blue line under the active tab. Nothing at that boundary has a
  // border - the active tab and #diff-ui are both var(--color-background) - so
  // it can only be the page gradient showing through a device-pixel row where
  // neither white paints. Whether such a row exists comes down to one number,
  // the bar's bottom edge minus the card's top edge, and measured across 14
  // viewports at three device pixel ratios that number is 0.813, 0.203 or
  // exactly 0.000 and never a whole pixel. At 0.000 the outcome belongs
  // entirely to the engine's sub-pixel rounding - which is why a DPR 3 phone
  // can show a line a DPR 1 desktop does not, and why 390x844 on the Screenshot
  // tab, the exact case reported, measures 0.000.
  //
  // So take the margin out of the engine's hands instead of hoping two white
  // edges land on the same device row. A pixel of overlap covers the gradient
  // on any grid; measured the same way afterwards, the worst case over those 42
  // readings becomes exactly 1.000px.
  //
  // The other candidate was a white skirt under the active tab
  // (box-shadow: 0 1px 0) which would have touched nothing else, and it does not
  // work: the shadow hangs below the bar's last child and #diff-header's
  // overflow: auto - the thing enforcing its height cap - clips it. Measured
  // with the card held 3px away so the skirt and the card are separable, it
  // painted 0 device rows of the 3 it needs at 844x390 and 926x428, and 0 to 2
  // in the sticky modes. Recorded here so it is not proposed again.
  //
  // What the overlap costs, stated rather than discovered later: where the bar
  // is sticky it is invisible, and a device-pixel diff of the seam band at
  // 390x844 and DPR 3 says so exactly - zero differing pixels, because the bar
  // is opaque and paints over the card. Below the short-viewport breakpoint the
  // bar has no background of its own, so the card's white also reaches the
  // bottom pixel of the *inactive* tabs and the 5px gaps between them: 4374
  // device pixels at 844x390, gradient turning white. The tab row ends up
  // sitting flush on the card rather than floating a pixel above it, which is
  // how tabs normally meet their panel and is the same continuity the active
  // tab was asked for.
  //
  // Scoped to the diff page deliberately. diff.css is NOT diff-page-only - it
  // is also served to the preview page (blueprint/ui/preview.py) and the
  // extract page (processors/extract.py), and both have a #diff-ui of their own
  // with no bar above it to absorb the pixel. Only difference.py sets the
  // difference-page class.
  #diff-ui {
    margin-top: -1px;
  }
}

#diff-header {
  position: sticky;
  // Sits directly under the now-sticky top menu. The 0 fallback (JS off) just
  // slides this under the bar - the same degradation the minimap already takes.
  top: var(--app-header-height, 0px);
  z-index: 20;
  // section.content insets its children by $common-gap so they clear the left
  // rail, while the top menu above stays flush against it. A bar that paints
  // the page's own backdrop therefore leaves an 8.8px strip of real page
  // background down each side, and on a device those strips read as mismatched
  // borders. Cancel the inset rather than try to blend across it: with no
  // gutter there is nothing left to keep aligned, and the flush right edge is
  // what page-surface-gradient anchors its copy of the page gradient to. The
  // controls do not move - the bar grows outwards by exactly the margin it
  // takes back.
  //
  // The width has to come from align-self, not width: 100%. .content-main
  // centres its children, so an item is fit-content unless it stretches, and a
  // percentage width resolves against the parent without the negative margins -
  // it would leave the bar short by 17.6px.
  align-self: stretch;
  margin-left: -$common-gap;
  margin-right: -$common-gap;
  box-sizing: border-box;
  // Center children at their intrinsic width, the same way section.content does
  // for the non-sticky siblings it still lays out (align-items: center).
  // Two rows: the toolbar and the tabs.
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 0.25rem;
  // No bottom padding: the tab row is the bar's last child, and the active tab
  // and #diff-ui below it are both var(--color-background). 4px of gradient
  // between them reads as a seam across an otherwise continuous white surface -
  // the same tabs on the extract page, which are not in a bar, measure 0. The
  // top padding stays; nothing sits above the toolbar.
  padding: 0.25rem 1rem 0;
  // Keep the diff readable even with wrapped controls, zoom, or a short viewport.
  // The budget is for the whole sticky stack, so the top menu above comes out of
  // it - otherwise the two bars together take 64% of a 390px-tall landscape phone.
  //
  // svh, not dvh. dvh tracks the dynamic viewport, which on iOS Safari grows and
  // shrinks as the browser's own toolbar collapses and expands while you scroll:
  // the cap would then breathe mid-scroll, changing the header's height and
  // shifting everything below it, and each transition also fires resize and
  // re-runs the sticky measurement behind it. svh is defined as the
  // toolbar-expanded minimum and holds still for the life of the page, so the
  // budget is a constant. It is the smaller of the two, which is the safe side to
  // be wrong on for a cap. The plain vh line stays as the fallback for engines
  // without the new units.
  max-height: calc(50vh - var(--app-header-height, 0px));
  max-height: calc(50svh - var(--app-header-height, 0px));
  overflow: auto;

  // Same offset as `top` above: the bar's constant distance from the top of the
  // viewport. With JS off the var is absent and the copy is misaligned by the
  // top menu's height - the same tier of degradation `top` itself already takes.
  @include page-surface-gradient(var(--app-header-height, 0px));

  > * {
    // A centered flex item is sized to fit-content, which has a min-content
    // floor (the version <select> is as wide as its longest option). Without
    // this cap a narrow viewport would centre an over-wide child and spill it
    // out of both sides of the header.
    max-width: 100%;
  }

  // base.html's wrap detector decides body.wrapped-tabs by flipping the tab <ul>
  // to flex-wrap and seeing whether any tab lands on a second row - so what it
  // measures against is the width of .tabs. _tabs.scss says in upstream's own
  // words that .tabs has to take the full width of the centred column "so the
  // wrap-detector JS has the real available space to measure against", and the
  // two properties that would do it are commented out directly underneath. As
  // shipped, .tabs is fit-content inside any centred column, so the detector
  // measures a container that moves with the layout state it is judging: the
  // active tab's label is bold, and selecting the widest one ("Current
  // screenshot") grows .tabs by ~9px. In the band where that crosses the
  // available width the verdict flips per tab - measured here at 350, 355 and
  // 358px, where Text and Extract Data report one row and Current screenshot
  // reports three. iOS puts the same band at 390px because its fonts are wider,
  // which is how a phone showed one row in a screenshot and a vertical stack in
  // a video of the same page.
  //
  // Give the detector a fixed target on this page only. Un-commenting the lines
  // in _tabs.scss would fix it everywhere and change every page upstream owns;
  // this PR does not have the standing to do that.
  .tabs {
    align-self: stretch;
    // Never give up height to keep the controls whole - see #settings below.
    flex: none;

    // .tabs no longer shrink-wraps, so the grid would sit left-aligned in it.
    ul {
      justify-content: center;

      // Stretching the container fixes one side of the detector's comparison;
      // this fixes the other. `.active a { font-weight: bold }` in _tabs.scss
      // makes the row's width depend on which label is currently bold: at 355px
      // the Text and Extract states measure 332.9 and 330.5 against a 339.0
      // container and stay on one row, while Current screenshot - the widest
      // label - measures over it and wraps to three. Neutralising just that rule
      // collapses all three states to 330.5 and the flipping stops, which is what
      // identifies the weight as the variable rather than the container.
      //
      // So drop the bold here rather than reserve room for it. Reserving the bold
      // width on every tab (a hidden bold copy behind each label) also stabilises
      // it, but it makes the row ~14px wider in every state and that pushes 360px
      // - a common Android width that fits on one row today - into the stacked
      // layout. The active tab does not need the third signal: _tabs.scss already
      // gives it its own background-color and its own text colour.
      li.active a,
      li :target a {
        font-weight: inherit;
      }
    }
  }

  // The bar's height budget (max-height above) is smaller than its contents on a
  // landscape phone: iOS gives the two datetime <select>s enough intrinsic width
  // that From and To each take their own row, and From + To + Filters + tabs is
  // then taller than 50svh minus the top menu. With overflow: auto on the bar
  // itself the row that leaves the visible box is the last one - the tabs, which
  // are the page's navigation and have no scrollbar to advertise themselves. Measured in Chromium with no iOS emulation at 736x414, 667x375,
  // 780x360 and 844x330: the tab row sits outside #diff-header's own rect.
  //
  // So spend the budget on the row that can afford it. #settings is the only
  // child allowed to shrink, and it is what scrolls; the tab row never does and
  // is therefore always inside the bar at any viewport height. The shrink needs
  // min-height: 0 - a flex item's automatic minimum size is its content, which
  // is what would otherwise push the tabs back out.
  #settings {
    min-width: 0;
    display: flex;
    justify-content: center;
    flex: 0 1 auto;
    min-height: 0;
    overflow-y: auto;
    // Same reason the Filters popover carries it: a nested scroller inside a
    // sticky bar that chains its overscroll to the diff behind is worse than no
    // scroller at all on a touch screen.
    overscroll-behavior: contain;
  }

  // One toolbar row: From/To chips and their selects, the version arrows, and
  // the Filters toggle.
  #diff-form {
    display: flex;
    flex-wrap: wrap;
    align-items: center;
    justify-content: center;
    gap: 0.25rem 0.9rem;
    padding: 0.2rem 0.7rem;
    margin-bottom: 0;

    fieldset {
      margin: 0;
      padding: 0;
      border: 0;
    }

    // The From/To labels shrink to chips rather than hiding: display:none takes
    // the <label> out of the accessibility tree and the selects lose their
    // accessible name entirely, and two identically formatted datetime selects
    // side by side need the red/green cue sighted users already know. The
    // shipped width: 4rem is what makes them full-size plates. "From" is wider
    // than "To", which left-ragged the selects once they stack, so the floor is
    // wide enough for the longer word - it costs width only, never height.
    .from-to-label {
      width: auto;
      min-width: 2.4rem;
      text-align: center;
      font-size: 0.75rem;
      padding: 0.1rem 0.35rem;
      border-radius: 3px;
      line-height: 1.5;
    }
  }

  #keyboard-nav {
    display: flex;
    align-items: center;
    gap: 0.3rem;

    // The arrows speak for themselves at this size; the links keep the full
    // wording as aria-label and title (see diff.html).
    strong,
    .keyboard-nav-label {
      display: none;
    }
  }

  // Seven set-once options are a popover, not a permanent row of the bar. The
  // swap happens only once diff-overview.js has wired the toggle up, so with
  // scripting off the fieldset stays inline and submits as it does today.
  #diff-filters-toggle {
    display: none;
    font-size: 0.85rem;
    padding: 0.3em 0.8em;
  }

  &.diff-filters-js {
    #diff-filters-toggle {
      display: inline-block;
    }

    #diff-style {
      display: none;
    }
  }

  &.diff-filters-js.diff-filters-open {
    #diff-style {
      // fixed, not absolute: #diff-header carries overflow: auto to enforce the
      // 50svh cap above, which clips an absolutely positioned descendant at the
      // bar's bottom edge. The bar is sticky with no transform/filter/contain,
      // so it is not a containing block for fixed and the panel escapes the
      // clip. diff-overview.js parks it under the toggle.
      display: block;
      position: fixed;
      z-index: 25;
      min-width: 14rem;
      // diff-overview.js caps max-height to the room below the button that the
      // viewport actually has - on a landscape phone that is less than the
      // seven rows need. The rows past the cap have to stay reachable, and the
      // scroll must not chain out to the diff behind once they run out.
      overflow-y: auto;
      overscroll-behavior: contain;
      padding: 0.5rem 0.75rem;
      border-radius: 8px;
      box-shadow: 0 4px 14px rgba(0, 0, 0, .28);
      text-align: left;

      // The bar repaints the page's own backdrop; so must anything that has to
      // be opaque over the scrolling diff. This one is not pinned to an edge of
      // the viewport - diff-overview.js decides where it goes - so the same
      // file overwrites background-position from the coordinates it just set.
      // The declaration here is what a placement-less first paint falls back to.
      @include page-surface-gradient;
    }

    // Out-specifies #diff-form #diff-style > span's inline-block above.
    #diff-form #diff-style > span {
      display: block;
      padding: 0.2em 0;
    }
  }

  .diff-fieldset {
    min-width: 0;
    display: flex;
    justify-content: center;
    flex-wrap: wrap;
    gap: 0.5rem;

    > span {
      max-width: 100%;
      min-width: 0;
      gap: 0.25rem;
      // Size to content so From/To stay side-by-side on desktop (as they were
      // before the header existed); shrink and wrap only when the row can't fit.
      flex: 0 1 auto;
      display: flex;
      align-items: center;
      // A <select> keeps the intrinsic min-content width of its longest option
      // (min-width: 0 does not lower it), so label + select cannot fit a phone
      // viewport side by side. Let the label drop above it instead of forcing
      // the whole header wider than the screen.
      flex-wrap: wrap;
    }

    select {
      min-width: 0;
      max-width: 100%;
      flex: 1;
    }

    label {
      flex-shrink: 0;
    }
  }
}

// The one narrow-viewport breakpoint for the whole bar - title, fit and
// gutters all hang off it rather than letting magic numbers multiply.
//
// Every selector below carries an ID on purpose. The rules it has to beat are
// written above as `#diff-header .diff-fieldset > span` and friends, and a
// single ID outranks any number of classes, so a class-only override loses
// silently and the chain goes on shrink-wrapping. Please don't tidy the IDs
// away.
@media (max-width: 700px) {
  // Once the From/To chip takes inline width the <select> clips its own
  // displayed value, and two snapshots from the same day differ only by the
  // meridiem - so they read identically while closed. Shrinking the font alone
  // cannot fix that: #settings, #diff-form, .diff-fieldset and the span are all
  // sized to max-content, which *is* the select's text, so the container
  // shrinks by exactly as much as the text does and the headroom stays pinned
  // at zero at every font size. Pin the chain to the row first; only then does
  // the smaller font buy anything.
  #diff-header > #settings {
    width: 100%;
  }

  #diff-header #diff-form {
    width: 100%;
    box-sizing: border-box;
    // 16px of bar gutter plus 11.2px of form gutter a side is 54px of a 390px
    // row spent on nothing.
    padding-left: 0.2rem;
    padding-right: 0.2rem;
  }

  #diff-header {
    padding-left: 0.5rem;
    padding-right: 0.5rem;
  }

  #diff-header #diff-form > .diff-fieldset {
    flex: 1 1 100%;
  }

  #diff-header .diff-fieldset > span {
    flex: 1 1 100%;
  }

  // With the chain pinned the select holds its width, so this is what actually
  // buys the room. The worst realistic English value - a two-digit day, the
  // longest month and a two-digit hour - still clips at 0.8rem.
  #diff-header .diff-fieldset select {
    font-size: 0.75rem;
    padding-left: 0.3em;
    padding-right: 0.3em;
  }
}

#diff-ui {

  background: var(--color-background);
  padding: 1rem;
  border-radius: 5px;

  @media (min-width: 767px) {
    min-width: 50%;
  }

  // The first tab 'text' diff
  #text {
    font-size: 11px;
  }

  pre {
    white-space: break-spaces;
    overflow-wrap: anywhere;
  }


  h1 {
    display: inline;
    font-size: 100%;
  }

  #result {
    white-space: pre-wrap;
    word-break: break-word;
    overflow-wrap: break-word;
  }


  .source {
    position: absolute;
    right: 1%;
    top: .2em;
  }

  @-moz-document url-prefix() {
    body {
      height: 99%;
      /* Hide scroll bar in Firefox */
    }
  }

  td#diff-col div {
    text-align: justify;
    white-space: pre-wrap;
  }

  .ignored {
    background-color: #ccc;
    /*  border: #0d91fa 1px solid; */
    opacity: 0.7;
  }

  .triggered {
    background-color: #1b98f8;
  }

  /* ignored and triggered? make it obvious error */
  .ignored.triggered {
    background-color: #ff0000;
  }

  .tab-pane-inner#screenshot {
    text-align: center;

    img {
      max-width: 99%;
    }
  }


  // resets button margin to 0px
  .pure-form button.reset-margin {
    margin: 0px;
  }

  .diff-fieldset {
    display: flex;
    align-items: center;
    gap: 4px;
    flex-wrap: wrap;
  }


  ul#highlightSnippetActions {
    list-style-type: none;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 1.5rem;
    flex-wrap: wrap;
    padding: 0;
    margin: 0;

    li {
      display: flex;
      flex-direction: column;
      align-items: center;
      text-align: center;
      padding: 0.5rem;
      gap: 0.3rem;

      button, a {
        white-space: nowrap;
      }
    }

    span {
      font-size: 0.8rem;
      color: var(--color-text-input-description);
    }
  }

  #cell-diff-jump-visualiser {
    display: flex;
    flex-direction: row;
    gap: 1px;
    background: var(--color-background);
    border-radius: 3px;
    overflow-x: hidden;
    position: sticky;
    top: calc(var(--app-header-height, 0px) + var(--diff-header-height, 0px));
    z-index: 10;
    padding-top: 1rem;
    padding-bottom: 1rem;
    justify-content: center;

    > div {
      flex: 1;
      min-width: 1px;
      max-width: 10px;
      height: 10px;
      background: var(--color-background-button-cancel);
      opacity: 0.3;
      border-radius: 1px;
      transition: opacity 0.2s;
      position: relative;

      &.deletion {
        background: #b30000; // Red for deletions
        opacity: 1;
      }

      &.insertion {
        background: #406619; // Green for insertions
        opacity: 1;
      }

      &.note {
        background: #406619; // Orange for changed/notes
        opacity: 1;
      }

      &.mixed {
        background: linear-gradient(to right, #b30000 50%, #406619 50%); // Half red, half green
        opacity: 1;
      }

      &.current-position::after {
        content: '';
        position: absolute;
        bottom: -6px;
        left: 50%;
        transform: translateX(-50%);
        width: 0;
        height: 0;
        border-left: 4px solid transparent;
        border-right: 4px solid transparent;
        border-bottom: 4px solid var(--color-text);
      }

      &:hover {
        opacity: 0.8;
        cursor: pointer;
      }
    }
  }
}

#text-diff-heading-area {
  .snapshot-age {
    padding: 4px;
    margin: 0.5rem 0;
    background-color: var(--color-background-snapshot-age);
    border-radius: 3px;
    font-weight: bold;
    margin-bottom: 4px;

    &.error {
      background-color: var(--color-error-background-snapshot-age);
      color: var(--color-error-text-snapshot-age);
    }
    > * {
      padding-right: 1rem;
    }
  }
}

// Placed last on purpose. Several of these rules out-specify nothing - they
// tie with the rule they are overriding, and a tie is decided by source
// order. The minimap's sticky offset is written further down this file as
// `#diff-ui #cell-diff-jump-visualiser`, so a block that sits above it loses
// silently. Keep this one at the bottom.
//
// A phone held sideways is the one place the sticky design cannot pay for
// itself. 50svh of a 390px-tall viewport is 195px, the top menu takes 55 of it,
// and what is left has to hold From, To, Filters and the tab row - three of
// those on their own lines, because iOS gives the two datetime selects enough
// width that From and To cannot share one. #settings shrinking and scrolling
// (see above) keeps the tabs inside the bar, but a bar you have to scroll
// *inside* to reach half its controls is still a bar in the way, and no amount
// of trimming decoration finds 195px.
//
// So stop compensating for the budget here and give up the budget instead.
// Below 500px of viewport height both bars are ordinary static blocks: no
// height cap, no inner scroller, title and every control present at once, and
// the page scrolls as one document. The trade is the sticky guarantee itself -
// the controls and the tab row scroll away with the diff, so switching tabs
// means scrolling back up - which is the right side to be wrong on when the
// alternative is controls you cannot see. Portrait is untouched.
//
// Keyed on viewport height rather than orientation: a short desktop window has
// the identical problem for the identical reason.
@media (max-height: 500px) {
  body.difference-page .header {
    // Not a new state: parts/_top_menu.scss ships .header with its sticky
    // commented out, so this is the position every other page's top menu is
    // already in. z-index goes inert along with it, which hands the mobile
    // drawer's 10000 back to the root stacking context.
    position: static;
    // Nothing scrolls underneath a static bar, so it neither needs its
    // pre-composited copy of the page gradient nor may keep it: the copy is
    // aligned by pushing it up by the bar's own *constant* viewport offset, and
    // a bar that scrolls has no constant offset. It would slide out of phase
    // with body::after's fixed layer and read as a moving seam. The shorthand,
    // not background-image - it resets size, origin and position too.
    background: none;
  }

  #diff-header {
    position: static;
    // The cap and the scroller are what the sticky design pays for its
    // guarantee that the diff keeps half the viewport. There is no longer a
    // guarantee to pay for.
    max-height: none;
    overflow: visible;
    background: none;

    #settings {
      // Same: it only shrank and scrolled to keep the tab row inside the cap.
      min-height: auto;
      overflow-y: visible;
    }
  }

  // .tab-pane-inner's scroll-margin-top is deliberately NOT overridden here,
  // and dropping it to a bare 1rem is a trap worth naming. It reads as an
  // allowance for pinned chrome, so with nothing pinned it looks like dead
  // weight - but upstream's tabs.js rewrites an empty hash to the first tab's
  // (tabs.js:15) and the browser then jumps to that pane on load, before any
  // of this is a choice. At 1rem that jump lands with the whole static bar
  // already scrolled off the top: measured -175.8px at 844x390, a landscape
  // page that opens with no controls on it at all. The existing formula is the
  // right number in both modes for two different reasons - in the sticky one it
  // clears chrome that is pinned over the pane, in the static one it keeps
  // chrome that sits above the pane on screen. Leave it alone.

  // The minimap is sticky inside the diff card, offset to sit directly below
  // the sticky stack. With that stack gone its offset would pin it a top menu
  // plus a whole toolbar down the viewport - past halfway on a 390px-tall one,
  // a strip floating in mid-screen beneath nothing. It is still worth pinning;
  // pin it to the viewport, which is now free.
  #diff-ui #cell-diff-jump-visualiser {
    top: 0;
  }
}