frontend: sidebar rework, add in chat

frontend/src/assets/main.css

@@ -13,7 +13,10 @@ main {
   overflow: auto;
 }
 
-main section {
+.row { display: flex; flex-direction: row; flex: 1; }
+.column { display: flex; flex-direction: column; flex: 1; }
+
+main section, .sidebar section {
   margin: 1em;
   padding: 1em;
   border: 1px solid var(--color-border);
@@ -21,15 +24,6 @@ main section {
   background-color: var(--color-surface);
 }
 
-.main-sidebar {
-  height: 100dvh;
-  display: flex;
-  flex-direction: column;
-  position: relative;
-  z-index: var(--z-index-sidebar);
-  background-color: var(--color-background);
-}
-
 .main-header {
   height: var(--header-height);
   border-bottom: 1px solid var(--color-border);
@@ -62,6 +56,12 @@ button.hollow:hover {
   border: none;
 }
 
+button.icon {
+  width: 3em;
+  height: 3em;
+  padding: 0;
+}
+
 button:hover {
   color: var(--color-heading);
   border-color: var(--color-border-hover);