First commit

frontend/app/assets/css/_mixins.scss

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+// Shared shapes the rest of the design is cut from. Colours stay CSS custom
+// properties throughout — [data-theme]/[data-accent] swap them at runtime.
+
+// the dark backdrop a popup opens onto ($pad-y: how far down the sheet sits)
+@mixin overlay($z, $pad-y: clamp(56px, 13vh, 132px)) {
+  position: fixed;
+  inset: 0;
+  z-index: $z;
+  display: flex;
+  justify-content: center;
+  align-items: flex-start;
+  padding: $pad-y 16px 16px;
+  background: color-mix(in srgb, #05070d 55%, transparent);
+  backdrop-filter: blur(3px);
+}
+
+// the paper dropped under a backdrop
+@mixin sheet($w, $max-h: null) {
+  display: flex;
+  flex-direction: column;
+  width: min($w, 100%);
+  @if $max-h {
+    max-height: $max-h;
+  }
+  border: 1px solid var(--border);
+  border-radius: 16px;
+  background: var(--bg-elev);
+  box-shadow: var(--shadow-lg);
+  overflow: hidden;
+}
+
+// a popup's title row: the title, and the × at the end of it
+@mixin sheet-head {
+  display: flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 12px;
+  padding: 13px 14px 13px 18px;
+  border-bottom: 1px solid var(--border);
+}
+
+@mixin sheet-title {
+  margin: 0;
+  font-size: 1.02rem;
+  font-weight: 700;
+}
+
+// the scrolling middle of a popup
+@mixin sheet-body($pad: 18px) {
+  flex: 1;
+  min-height: 0;
+  overflow-y: auto;
+  padding: $pad;
+  scrollbar-width: thin;
+}
+
+// the opening animation every popup shares: the backdrop fades, the sheet
+// slides in from the edge it hangs nearest ($offset is where it starts)
+@mixin popup-anim($name, $sheet, $dur, $sheet-move, $offset) {
+  .#{$name}-enter-active,
+  .#{$name}-leave-active {
+    transition: opacity $dur ease;
+
+    #{$sheet} { transition: $sheet-move; }
+  }
+
+  .#{$name}-enter-from,
+  .#{$name}-leave-to {
+    opacity: 0;
+
+    #{$sheet} { transform: translateY($offset) scale(0.98); }
+  }
+}
+
+// a menu that drops from a button: the popups' paper, on a hinge
+// ($overflow: `auto` once it caps at a max-height; `visible` may not clip
+// a nested dropdown)
+@mixin dropdown-panel($z: 20, $overflow: auto) {
+  position: absolute;
+  z-index: $z;
+  top: calc(100% + 6px);
+  padding: 6px;
+  overflow-y: $overflow;
+  border-radius: 12px;
+  border: 1px solid var(--border);
+  background: var(--bg-elev);
+  box-shadow: var(--shadow-lg);
+}
+
+// a row inside a dropdown: full width, icon then label, an accent wash on hover
+@mixin menu-row($pad, $gap, $fs: 0.85rem) {
+  display: flex;
+  align-items: center;
+  gap: $gap;
+  width: 100%;
+  padding: $pad;
+  border-radius: 8px;
+  color: var(--text);
+  font-size: $fs;
+  font-weight: 600;
+  transition: background-color 0.12s;
+}
+
+// the small caps label over a section of the interface
+@mixin eyebrow($fs: 0.72rem, $fw: 750, $ls: 0.1em, $color: var(--faint)) {
+  font-size: $fs;
+  font-weight: $fw;
+  text-transform: uppercase;
+  letter-spacing: $ls;
+  color: $color;
+}
+
+// the account's face in a circle: an initial, or a picture laid over it
+@mixin avatar($size, $fs) {
+  display: grid;
+  place-items: center;
+  flex-shrink: 0;
+  width: $size;
+  height: $size;
+  border-radius: 50%;
+  background: color-mix(in srgb, var(--accent) 14%, transparent);
+  color: var(--accent);
+  font-size: $fs;
+  font-weight: 800;
+  line-height: 1;
+  overflow: hidden;
+
+  img {
+    display: block;
+    width: 100%;
+    height: 100%;
+    border-radius: 50%;
+    object-fit: cover;
+  }
+}
+
+// a square target that centres its icon
+@mixin icon-target($size, $radius) {
+  display: grid;
+  place-items: center;
+  flex-shrink: 0;
+  width: $size;
+  height: $size;
+  border-radius: $radius;
+}
+
+// a quiet row that warms on hover (nav links, icon buttons)
+@mixin hover-row {
+  transition: color 0.15s, background-color 0.15s;
+
+  &:hover { color: var(--text); background: var(--surface-2); }
+}
+
+// a row of choices styled as one segmented control
+@mixin segmented {
+  display: inline-flex;
+  gap: 4px;
+  padding: 4px;
+  border: 1px solid var(--border);
+  border-radius: 12px;
+  background: var(--surface-2);
+}
+
+@mixin segmented-tab($pad, $fs) {
+  padding: $pad;
+  border-radius: 9px;
+  background: transparent;
+  color: var(--muted);
+  font-size: $fs;
+  font-weight: 600;
+  transition: color 0.15s, background-color 0.15s, box-shadow 0.15s;
+
+  &:hover { color: var(--text); }
+
+  &.active { background: var(--surface); color: var(--text); box-shadow: var(--shadow-sm); }
+}
+
+// the loading shimmer a skeleton wears
+@mixin shimmer {
+  background: linear-gradient(
+    100deg,
+    var(--surface) 40%,
+    color-mix(in srgb, var(--surface) 55%, var(--text) 9%) 50%,
+    var(--surface) 60%
+  );
+  background-size: 200% 100%;
+  animation: shimmer 1.4s infinite linear;
+}
+
+// paint text with a gradient between the two accents
+@mixin gradient-text($angle: 90deg) {
+  background: linear-gradient($angle, var(--accent), var(--accent-2));
+  -webkit-background-clip: text;
+  background-clip: text;
+  color: transparent;
+}
+
+// a row of the book: no gutter along its edge (a book has none)
+@mixin no-scrollbar {
+  scrollbar-width: none;
+
+  &::-webkit-scrollbar { display: none; }
+}
+
+// the × that closes a page or a chip: faint, and turns danger on hover
+@mixin close-target {
+  &:hover {
+    color: var(--danger);
+    background: color-mix(in srgb, var(--danger) 10%, transparent);
+  }
+}