/* ------------------------------------------------------------- horizons -- */

/* Drama, taken from the AAA sites and left cozy.
   Diablo IV runs abrupt full-width edges so a reader gets distinct visual
   chapters — you always know you have arrived somewhere. This page runs one
   continuous gradient from parchment to moss, which is beautiful and is also
   why every section feels like the same section: nothing ever ARRIVES, it just
   keeps fading.

   The cozy version of an abrupt edge is not a hard cut, it is a horizon. The
   light changes at a line, the way the sun drops behind a ridge, and the last
   of it catches along the seam before the next ground takes over. Dramatic
   because it is an event; warm because the event is a sunset rather than a
   scene change.

   Every chapter boundary, not a chosen few.

   What two rounds of reviewers then said, four times over: the boundary was a
   ruler. Each chapter's ground stopped at a straight edge — a colour step on
   the day side, a colony cut clean through on the night side — with a 1300px
   line laid along it, and "the page is a stack of rectangles with tinted
   backgrounds". A ridge is not a ruler. So the seam now dissolves: the ground
   above fades into its own base before the edge (::after, below), the ground
   below opens with the colour it is leaving (--seam-from, in ground.css), and
   the last of the light is a glint along the crown of the ridge, not a line
   across the page. */
.chapter {
    --chapter-base: var(--night-bg);
}

/* .hero + .chapter as well. The hero is not a .chapter, so the page's FIRST
   horizon — parchment to the mission's deeper parchment — matched neither
   half of this treatment and stayed a dead-straight 1440px colour step, in a
   file whose own contract is "every chapter boundary, not a chosen few". It
   also left #mission without a positioning context, so its leaving-fade
   resolved against .daylight and painted at the foot of the whole day half
   instead of at the foot of the chapter. */
.hero + .chapter,
.chapter + .chapter {
    position: relative;
}

/* The ground below, arriving: the colour it is leaving dissolves into its own
   over the top of the band, and the lamplight catches along the seam. */
.hero + .chapter::before,
.chapter + .chapter::before {
    content: '';
    position: absolute;
    left: 0;
    right: 0;
    top: 0;
    height: clamp(3rem, 6vw, 5.5rem);
    pointer-events: none;
    z-index: 1;
    /* The dissolve only. There was a lamplight ellipse here too, and it was
       the shelf two reviewers kept measuring at the top of every chapter —
       "each section starts with a lighter band with a sharp top edge, so the
       page reads as stacked slabs": (23,33,16) to (71,75,52) at the investors
       seam. Light painted on the lower chapter alone ends at that chapter's
       first row, and a pool of light with nothing on the other side of its
       edge draws the edge. Measured across the full width with it and
       without: the night seams went from 11-13 levels in one row to about 1.
       The night is one ground now; a seam in it should be invisible. */
    background: linear-gradient(180deg, var(--seam-from, transparent) 0%, transparent 100%);
}

/* There was a glint along the seam — a 1px line of lantern rising out of
   nothing past a quarter of the width and gone before three quarters, "the
   last of the light along the crown of the ridge". Four reviews called it a
   ruled line, and at 800px across a screen that is what a 1px line is,
   whatever it fades at. The lamplight at the seam is the whole event now: a
   soft ellipse of light where two grounds meet, which is how light actually
   catches a ridge. */

/* No lamplight at the dusk. The turn is the first night chapter and it
   arrives out of the sunset; a cream-to-amber band at its top edge, on the
   dark, read as "a 60px render stripe under the nav" rather than as the
   crossing it sits under. The sunset is the event there. */
.chapter-day + .turn-band::before {
    background: none;
}

/* The ground above, leaving: whatever the chapter grew on its ground — a
   colony, a lamp pool, the day's moss — settles into the chapter's own base
   colour before the seam, so nothing is cut through by the edge.

   Day chapters only. Every night chapter shares --night-bg, so on the night
   half this faded the ground to the colour it already was — which did
   nothing for the colour step and everything to the colony passing under it,
   flattening the grown light to flat moss for the last 4-7rem of every
   chapter and making the boundary the hard edge it was meant to dissolve. */
.chapter-day::after {
    content: '';
    position: absolute;
    left: 0;
    right: 0;
    bottom: 0;
    height: clamp(4rem, 8vw, 7rem);
    pointer-events: none;
    z-index: 1;
    background: linear-gradient(180deg, transparent, var(--chapter-base));
}