navbar: Hide view, channel descriptions at small viewports.

This is an attempt to fix somewhat #33685. More finesse can
probably be done in the area, but hiding descriptions on a title-
by-title basis will be non-trivial.

web/src/css_variables.ts

@@ -38,6 +38,7 @@ export const container_breakpoints = {
     cq_xl_min: xl / base_em_px + "em",
     cq_lg_min: lg / base_em_px + "em",
     cq_md_min: md / base_em_px + "em",
+    cq_sm_min: sm / base_em_px + "em",
     cq_mm_min: mm / base_em_px + "em",
 };
 

web/styles/zulip.css

@@ -1723,6 +1723,12 @@ body:not(.hide-left-sidebar) {
     }
 }
 
+@container header-container (width <= $cq_sm_min) {
+    .narrow_description {
+        display: none;
+    }
+}
+
 /* Begin fallback media queries. */
 @media (width < $xl_min) {
     .without-container-query-support {
@@ -1804,6 +1810,14 @@ body:not(.hide-left-sidebar) {
     }
 }
 
+@media (width <= $sm_min) {
+    .without-container-query-support {
+        .narrow_description {
+            display: none;
+        }
+    }
+}
+
 /* End fallback media queries. */
 
 /* Begin viewport state queries. */