3syisgbyq: Add a reusable bottom sheet with the comments and composer sheets on the phone feed

src/styles/sheet.css

@@ -0,0 +1,93 @@
+/*
+ * Bottom sheets (spec "Sheets"). Ported from the mockup's .psheet, .grab,
+ * .psheet-h and .ph-bg rules, plus the `.mx.sheet .cmp` composer rules. Tokens
+ * only. The sheet sits inside the phone feed (.reel-feed), over the dock.
+ */
+@keyframes sheet-up { from { transform: translateY(100%); } to { transform: none; } }
+@keyframes sheet-fade { from { opacity: 0; } to { opacity: 1; } }
+
+.sheet-bg {
+  position: absolute;
+  inset: 0;
+  z-index: 55;
+  appearance: none;
+  border: 0;
+  padding: 0;
+  cursor: pointer;
+  background: color-mix(in srgb, var(--bg), transparent 50%);
+  -webkit-backdrop-filter: blur(3px);
+  backdrop-filter: blur(3px);
+  animation: sheet-fade .3s both;
+}
+.sheet {
+  position: absolute;
+  left: 0;
+  right: 0;
+  bottom: 0;
+  z-index: 60;
+  display: flex;
+  flex-direction: column;
+  gap: 10px;
+  max-height: 78%;
+  padding: 10px 14px calc(24px + env(safe-area-inset-bottom, 0px));
+  background: var(--bg);
+  color: var(--ink);
+  border-radius: 26px 26px 0 0;
+  box-shadow: 0 -20px 50px -10px color-mix(in srgb, var(--neu-d), transparent 45%), inset 0 1px 0 var(--line);
+  animation: sheet-up .45s cubic-bezier(.2,.9,.25,1) both;
+  outline: none;
+}
+.sheet-grab {
+  flex: none;
+  width: 40px;
+  height: 5px;
+  margin: 0 auto 4px;
+  border-radius: 3px;
+  background: var(--line-2);
+}
+.sheet-h { flex: none; display: flex; align-items: center; justify-content: space-between; gap: 8px; }
+.sheet-h h2 { margin: 0; font-size: 25px; line-height: 1.2; }
+.sheet-x {
+  appearance: none;
+  flex: none;
+  width: 44px;
+  height: 44px;
+  margin: 0;
+  padding: 0;
+  border: 0;
+  border-radius: var(--r-ctl);
+  display: grid;
+  place-items: center;
+  background: transparent;
+  color: var(--ink-2);
+  cursor: pointer;
+  transition: background-color .2s, color .2s;
+}
+.sheet-x svg { width: 20px; height: 20px; }
+@media (hover: hover) { .sheet-x:hover { background: var(--tile-2); color: var(--ink); } }
+.sheet-x:focus-visible { outline: 2px solid var(--ink); outline-offset: 2px; }
+.sheet-body { min-height: 0; display: flex; flex-direction: column; gap: 10px; overflow-y: auto; }
+
+/* Comments sheet: the shared comments panel without its inline-card chrome. */
+.sheet-comments .post-cm { margin: 0; padding: 0; border-top: 0; animation: none; flex: 1; min-height: 0; }
+.sheet-comments .post-cm-list { overflow-y: auto; min-height: 60px; }
+.sheet-comments .post-cm-form { flex: none; }
+.sheet-comments .post-cm-form input { font-size: 16px; }
+
+/* Composer sheet: the desktop composer, borderless, with a 150px text area. */
+.sheet-composer { max-height: 92%; }
+.sheet-composer .sheet-body { overflow: visible; }
+.sheet-composer .composer,
+.sheet-composer .composer.composer-open { margin: 0; padding: 0; background: transparent; box-shadow: none; }
+.sheet-composer .composer textarea,
+.sheet-composer .composer.composer-open textarea { height: 150px; font-size: 16px; }
+.sheet-composer .composer-bar { flex-wrap: wrap; }
+.sheet-composer .composer-kbd { display: none; }
+/* The popover anchors to the whole composer (not the emoji button) so it fits a phone: full width, just above the toolbar. */
+.sheet-composer .composer-emoji-wrap { position: static; }
+.sheet-composer .composer-emoji { left: 0; right: 0; width: auto; top: auto; bottom: 64px; }
+.sheet-composer .composer-att.composer-att-indent { margin-left: 0; }
+
+@media (prefers-reduced-motion: reduce) {
+  .sheet, .sheet-bg { animation: none !important; }
+}