diff --git a/packages/ui/src/components/instance/instance-shell2.tsx b/packages/ui/src/components/instance/instance-shell2.tsx
index 84e55578..0263d343 100644
--- a/packages/ui/src/components/instance/instance-shell2.tsx
+++ b/packages/ui/src/components/instance/instance-shell2.tsx
@@ -81,7 +81,8 @@ interface InstanceShellProps {
 }
 
 const InstanceShell2: Component<InstanceShellProps> = (props) => {
-  const { t } = useI18n()
+  const { t, locale } = useI18n()
+  const isRTL = () => locale() === "he"
 
   const [sessionSidebarWidth, setSessionSidebarWidth] = createSignal(DEFAULT_SESSION_SIDEBAR_WIDTH)
   const [rightDrawerWidth, setRightDrawerWidth] = createSignal(
@@ -371,7 +372,7 @@ const InstanceShell2: Component<InstanceShellProps> = (props) => {
           sx={{
             width: `${sessionSidebarWidth()}px`,
             flexShrink: 0,
-            borderRight: "1px solid var(--border-base)",
+            borderInlineEnd: "1px solid var(--border-base)",
             backgroundColor: "var(--surface-secondary)",
             height: "100%",
             minHeight: 0,
@@ -413,7 +414,7 @@ const InstanceShell2: Component<InstanceShellProps> = (props) => {
     const modalProps = container ? { container: container as Element } : undefined
     return (
       <Drawer
-        anchor="left"
+        anchor={isRTL() ? "right" : "left"}
         variant="temporary"
         open={leftOpen()}
         onClose={closeLeftDrawer}
@@ -422,7 +423,7 @@ const InstanceShell2: Component<InstanceShellProps> = (props) => {
           "& .MuiDrawer-paper": {
             width: isPhoneLayout() ? "100vw" : `${sessionSidebarWidth()}px`,
             boxSizing: "border-box",
-            borderRight: isPhoneLayout() ? "none" : "1px solid var(--border-base)",
+            borderInlineEnd: isPhoneLayout() ? "none" : "1px solid var(--border-base)",
             backgroundColor: "var(--surface-secondary)",
             backgroundImage: "none",
             color: "var(--text-primary)",
@@ -480,7 +481,7 @@ const InstanceShell2: Component<InstanceShellProps> = (props) => {
           sx={{
             width: `${rightDrawerWidth()}px`,
             flexShrink: 0,
-            borderLeft: "1px solid var(--border-base)",
+            borderInlineStart: "1px solid var(--border-base)",
             backgroundColor: "var(--surface-secondary)",
             height: "100%",
             minHeight: 0,
@@ -523,7 +524,7 @@ const InstanceShell2: Component<InstanceShellProps> = (props) => {
     const modalProps = container ? { container: container as Element } : undefined
     return (
       <Drawer
-        anchor="right"
+        anchor={isRTL() ? "left" : "right"}
         variant="temporary"
         open={rightOpen()}
         onClose={closeRightDrawer}
@@ -532,7 +533,7 @@ const InstanceShell2: Component<InstanceShellProps> = (props) => {
           "& .MuiDrawer-paper": {
             width: isPhoneLayout() ? "100vw" : `${rightDrawerWidth()}px`,
             boxSizing: "border-box",
-            borderLeft: isPhoneLayout() ? "none" : "1px solid var(--border-base)",
+            borderInlineStart: isPhoneLayout() ? "none" : "1px solid var(--border-base)",
             backgroundColor: "var(--surface-secondary)",
             backgroundImage: "none",
             color: "var(--text-primary)",
diff --git a/packages/ui/src/lib/i18n/index.tsx b/packages/ui/src/lib/i18n/index.tsx
index c65e5bc3..4632d096 100644
--- a/packages/ui/src/lib/i18n/index.tsx
+++ b/packages/ui/src/lib/i18n/index.tsx
@@ -210,6 +210,11 @@ export const I18nProvider: ParentComponent = (props) => {
     document.documentElement.lang = activeLocale
   })
 
+  const RTL_LOCALES = new Set<Locale>(["he"])
+  createEffect(() => {
+    document.documentElement.dir = RTL_LOCALES.has(locale()) ? "rtl" : "ltr"
+  })
+
   onCleanup(() => {
     globalMessages = previousGlobalMessages
     globalLocale = previousGlobalLocale
diff --git a/packages/ui/src/styles/components/directory-browser.css b/packages/ui/src/styles/components/directory-browser.css
index bdbccbc0..cc727afa 100644
--- a/packages/ui/src/styles/components/directory-browser.css
+++ b/packages/ui/src/styles/components/directory-browser.css
@@ -124,7 +124,7 @@
   display: flex;
   align-items: center;
   gap: var(--space-md);
-  text-align: left;
+  text-align: start;
   background: transparent;
   border: none;
   color: var(--text-primary);
diff --git a/packages/ui/src/styles/components/settings-screen.css b/packages/ui/src/styles/components/settings-screen.css
index 7f6abe56..31805bb9 100644
--- a/packages/ui/src/styles/components/settings-screen.css
+++ b/packages/ui/src/styles/components/settings-screen.css
@@ -43,7 +43,7 @@
   padding: 1.25rem;
   background:
     linear-gradient(180deg, color-mix(in oklab, var(--surface-secondary) 92%, var(--accent-primary) 8%), var(--surface-secondary));
-  border-right: 1px solid var(--border-base);
+  border-inline-end: 1px solid var(--border-base);
 }
 
 .settings-screen-nav-header {
@@ -121,6 +121,9 @@
   color: var(--text-primary);
   transform: translateX(2px);
 }
+[dir="rtl"] .settings-nav-button[data-selected="true"] {
+  transform: translateX(-2px);
+}
 
 .settings-nav-button-icon {
   width: 1rem;
@@ -360,7 +363,7 @@
   border: 1px solid var(--border-base);
   background: var(--surface-base);
   color: var(--text-primary);
-  text-align: left;
+  text-align: start;
   transition: border-color 140ms ease, background-color 140ms ease, box-shadow 140ms ease, transform 140ms ease;
   outline: none;
   cursor: pointer;
@@ -418,7 +421,7 @@
 }
 
 .settings-choice-check {
-  margin-left: auto;
+  margin-inline-start: auto;
   color: var(--accent-primary);
   opacity: 0;
 }
@@ -488,7 +491,7 @@
   .settings-screen-nav {
     gap: 0.75rem;
     padding: 1rem;
-    border-right: none;
+    border-inline-end: none;
     border-bottom: 1px solid var(--border-base);
   }
 
diff --git a/packages/ui/src/styles/messaging/message-base.css b/packages/ui/src/styles/messaging/message-base.css
index dc048055..fa9614dd 100644
--- a/packages/ui/src/styles/messaging/message-base.css
+++ b/packages/ui/src/styles/messaging/message-base.css
@@ -141,13 +141,13 @@
 
 .message-step-start {
   background-color: var(--message-assistant-bg);
-  border-left: 4px solid var(--message-assistant-border);
+  border-inline-start: 4px solid var(--message-assistant-border);
   margin-top: 0;
 }
 
 .message-step-finish {
   background-color: var(--message-assistant-bg);
-  border-left: 4px solid var(--message-assistant-border);
+  border-inline-start: 4px solid var(--message-assistant-border);
   margin: 0;
 }
 
@@ -172,7 +172,7 @@
   font-size: 9px;
   color: var(--text-muted);
   font-weight: var(--font-weight-medium);
-  margin-right: 0.35rem;
+  margin-inline-end: 0.35rem;
 }
 
 .message-step-heading {
@@ -335,12 +335,12 @@
 
 .message-step-start {
   background-color: var(--message-assistant-bg);
-  border-left: 4px solid var(--message-assistant-border);
+  border-inline-start: 4px solid var(--message-assistant-border);
 }
 
 .message-step-finish {
   background-color: var(--message-assistant-bg);
-  border-left: 4px solid var(--message-assistant-border);
+  border-inline-start: 4px solid var(--message-assistant-border);
 }
 
 .message-step-heading {
@@ -390,7 +390,7 @@
 .message-reasoning-card {
   --reasoning-border-color: var(--border-strong, var(--border-base));
   background-color: var(--message-assistant-bg);
-  border-left: 4px solid var(--message-assistant-border);
+  border-inline-start: 4px solid var(--message-assistant-border);
   margin-top: 0;
   margin-bottom: 0;
   padding: 0;
diff --git a/packages/ui/src/styles/messaging/message-section.css b/packages/ui/src/styles/messaging/message-section.css
index 15ded9e5..7e6f2475 100644
--- a/packages/ui/src/styles/messaging/message-section.css
+++ b/packages/ui/src/styles/messaging/message-section.css
@@ -207,7 +207,7 @@
 
 .message-scroll-button-wrapper {
   position: absolute;
-  right: 1rem;
+  inset-inline-end: 1rem;
   bottom: 1rem;
   display: flex;
   flex-direction: column;
@@ -274,7 +274,7 @@
 }
 
 .message-quote-button + .message-quote-button {
-  border-left: 1px solid var(--list-item-highlight-border);
+  border-inline-start: 1px solid var(--list-item-highlight-border);
 }
 
 .message-quote-button:hover {
diff --git a/packages/ui/src/styles/messaging/message-selection.css b/packages/ui/src/styles/messaging/message-selection.css
index b6e7eb01..28e9df97 100644
--- a/packages/ui/src/styles/messaging/message-selection.css
+++ b/packages/ui/src/styles/messaging/message-selection.css
@@ -3,7 +3,7 @@
 .message-select-checkbox {
   width: 14px;
   height: 14px;
-  margin-right: 0.5rem;
+  margin-inline-end: 0.5rem;
   cursor: pointer;
   accent-color: var(--status-error);
   flex: 0 0 auto;
@@ -134,7 +134,7 @@
 }
 
 .message-delete-mode-menu {
-  right: 0;
+  inset-inline-end: 0;
   bottom: calc(100% + 6px);
   min-width: 150px;
   width: max-content;
diff --git a/packages/ui/src/styles/messaging/message-timeline.css b/packages/ui/src/styles/messaging/message-timeline.css
index 613b2220..78aeb927 100644
--- a/packages/ui/src/styles/messaging/message-timeline.css
+++ b/packages/ui/src/styles/messaging/message-timeline.css
@@ -20,7 +20,7 @@
   position: absolute;
   top: 0;
   bottom: 0;
-  right: 64px;
+  inset-inline-end: 64px;
   width: 1px;
   background-color: var(--border-muted);
   pointer-events: none;
@@ -32,7 +32,7 @@
   }
 
   .message-layout--with-timeline::after {
-    right: 40px;
+    inset-inline-end: 40px;
   }
 }
 
@@ -311,12 +311,12 @@
 
 /* Tool segments that are part of a group get a left accent border. */
 .message-timeline-group-child {
-  border-left: 3px solid color-mix(in oklab, var(--accent-primary) 35%, transparent);
+  border-inline-start: 3px solid color-mix(in oklab, var(--accent-primary) 35%, transparent);
 }
 
 /* The assistant "parent" at the bottom of a tool group gets the same border. */
 .message-timeline-group-parent {
-  border-left: 3px solid color-mix(in oklab, var(--accent-primary) 35%, transparent);
+  border-inline-start: 3px solid color-mix(in oklab, var(--accent-primary) 35%, transparent);
 }
 
 /* Extra spacing before the first tool in a group to separate from the
@@ -346,7 +346,7 @@
   /* Extend the overlay box into the stream so ribs are not relying on
      overflow-visible behavior (which is brittle around scroll containers). */
   --xray-overhang: calc(var(--max-rib-width, 50vw) + 84px);
-  left: calc(-1 * var(--xray-overhang));
+  inset-inline-start: calc(-1 * var(--xray-overhang));
   width: calc(100% + var(--xray-overhang));
   overflow: hidden;
   padding: 0.25rem;
@@ -374,10 +374,10 @@
 
 .message-timeline-xray-token-label {
   position: absolute;
-  right: 100%;
+  inset-inline-end: 100%;
   top: 50%;
   transform: translateY(-50%);
-  margin-right: 4px;
+  margin-inline-end: 4px;
   height: 1.5rem;
   display: flex;
   align-items: center;
@@ -403,16 +403,25 @@
     var(--status-success) calc(100% - var(--segment-weight) * 100%),
     var(--status-error) calc(var(--segment-weight) * 100%)
   );
-  border-radius: 3px 0 0 3px;
+  border-start-start-radius: 3px;
+  border-end-start-radius: 3px;
+  border-start-end-radius: 0;
+  border-end-end-radius: 0;
   transition: width 0.3s ease, background-color 0.3s ease;
   box-shadow: -2px 0 4px rgba(0, 0, 0, 0.25);
 }
+[dir="rtl"] .message-timeline-relative-bar {
+  box-shadow: 2px 0 4px rgba(0, 0, 0, 0.25);
+}
 
 .message-timeline-absolute-bar {
   height: 3px;
   width: calc(var(--segment-weight) * var(--max-rib-width, 50vw));
   background-color: var(--text-muted);
-  border-radius: 2px 0 0 2px;
+  border-start-start-radius: 2px;
+  border-end-start-radius: 2px;
+  border-start-end-radius: 0;
+  border-end-end-radius: 0;
   transition: width 0.3s ease;
   opacity: 0.5;
   position: relative;
@@ -425,7 +434,7 @@
 .message-timeline-absolute-bar-overflow::before {
   content: "";
   position: absolute;
-  left: -1px;
+  inset-inline-start: -1px;
   top: -3px;
   bottom: -3px;
   width: 3px;
diff --git a/packages/ui/src/styles/messaging/prompt-input.css b/packages/ui/src/styles/messaging/prompt-input.css
index 8cbfb796..bd8df62c 100644
--- a/packages/ui/src/styles/messaging/prompt-input.css
+++ b/packages/ui/src/styles/messaging/prompt-input.css
@@ -65,8 +65,8 @@
 .prompt-input-overlay {
   position: absolute;
   bottom: 1rem;
-  left: 0.75rem;
-  right: 0.75rem;
+  inset-inline-start: 0.75rem;
+  inset-inline-end: 0.75rem;
   display: flex;
   flex-wrap: wrap;
   gap: 0.5rem;
@@ -85,7 +85,7 @@
 .prompt-nav-buttons {
   position: absolute;
   top: 0.25rem;
-  right: 0.25rem;
+  inset-inline-end: 0.25rem;
   bottom: 0.25rem;
   display: flex;
   flex-direction: column;
diff --git a/packages/ui/src/styles/messaging/tool-call.css b/packages/ui/src/styles/messaging/tool-call.css
index 4c504b36..7c54fa36 100644
--- a/packages/ui/src/styles/messaging/tool-call.css
+++ b/packages/ui/src/styles/messaging/tool-call.css
@@ -5,7 +5,7 @@
 .tool-call-message {
   @apply flex flex-col gap-2 p-3 w-full;
   background-color: var(--message-tool-bg);
-  border-left: 4px solid var(--message-tool-border);
+  border-inline-start: 4px solid var(--message-tool-border);
   color: inherit;
 }
 
@@ -105,7 +105,7 @@
 .tool-call-header-toggle::before {
   content: "▶";
   font-size: 11px;
-  margin-right: 0.35rem;
+  margin-inline-end: 0.35rem;
   color: var(--text-secondary);
 }
 
@@ -168,26 +168,26 @@
 }
 
 .tool-call-summary[data-tool-icon=""]::before {
-  margin-right: 0;
+  margin-inline-end: 0;
   content: "";
 }
 
 .tool-call-summary[data-tool-icon]:not([data-tool-icon=""])::before {
-  margin-right: 0.35rem;
+  margin-inline-end: 0.35rem;
 }
 
 /* ToolState uses status="completed"; keep "success" as a legacy alias. */
 .tool-call-status-completed,
 .tool-call-status-success {
-  border-left: 3px solid var(--status-success);
+  border-inline-start: 3px solid var(--status-success);
 }
 
 .tool-call-status-error {
-  border-left: 3px solid var(--status-error);
+  border-inline-start: 3px solid var(--status-error);
 }
 
 .tool-call-status-running {
-  border-left: 3px solid var(--status-warning);
+  border-inline-start: 3px solid var(--status-warning);
 }
 
 .tool-call-status-running .tool-call-status {
@@ -195,7 +195,7 @@
 }
 
 .tool-call-status-pending {
-  border-left: 3px solid var(--accent-primary);
+  border-inline-start: 3px solid var(--accent-primary);
 }
 
 .tool-call-status-pending .tool-call-summary {
@@ -267,7 +267,7 @@
 .tool-call-io-toggle::before {
   content: "▶";
   font-size: 11px;
-  margin-right: 0.35rem;
+  margin-inline-end: 0.35rem;
   color: var(--text-secondary);
 }
 
@@ -393,7 +393,7 @@
 }
 
 .tool-call-awaiting-permission {
-  border-left-color: var(--status-warning);
+  border-inline-start-color: var(--status-warning);
 }
 
 .tool-call-permission {
@@ -484,7 +484,7 @@
 }
 
 .tool-call-permission-shortcuts .kbd {
-  margin-right: 0.25rem;
+  margin-inline-end: 0.25rem;
 }
 
 .tool-call-permission-queued-text {
@@ -693,8 +693,8 @@
   gap: var(--space-xs);
   max-height: calc(4 * var(--tool-call-line-unit, 1.4em));
   overflow-y: scroll;
-  padding-right: 0;
-  margin-right: 0;
+  padding-inline-end: 0;
+  margin-inline-end: 0;
   scrollbar-gutter: stable both-edges;
   scrollbar-width: thin;
 }
@@ -843,7 +843,7 @@
 
 .tool-call-error-content {
   background-color: var(--message-error-bg);
-  border-left: 3px solid var(--status-error);
+  border-inline-start: 3px solid var(--status-error);
   padding: 12px;
   margin: 8px 0;
   border-radius: 4px;
diff --git a/packages/ui/src/styles/messaging/tool-call/task.css b/packages/ui/src/styles/messaging/tool-call/task.css
index 83e435ac..d628d6fc 100644
--- a/packages/ui/src/styles/messaging/tool-call/task.css
+++ b/packages/ui/src/styles/messaging/tool-call/task.css
@@ -86,7 +86,7 @@
 .tool-call-task-summary .tool-call::before {
   content: "";
   position: absolute;
-  left: 0;
+  inset-inline-start: 0;
   top: 0;
   bottom: 0;
   width: 3px;
@@ -117,7 +117,7 @@
   align-items: center;
   gap: 0.4rem;
   padding: 0.35rem 0.5rem 0.35rem 0.75rem;
-  border-left: 2px solid var(--tool-call-border-color, var(--border-base));
+  border-inline-start: 2px solid var(--tool-call-border-color, var(--border-base));
   font-size: var(--font-size-sm);
   font-family: var(--font-family-mono);
   line-height: 1.35;
@@ -134,19 +134,19 @@
 }
 
 .tool-call-task-item[data-task-status="completed"] {
-  border-left-color: var(--status-success);
+  border-inline-start-color: var(--status-success);
 }
 
 .tool-call-task-item[data-task-status="running"] {
-  border-left-color: var(--status-warning);
+  border-inline-start-color: var(--status-warning);
 }
 
 .tool-call-task-item[data-task-status="pending"] {
-  border-left-color: var(--accent-primary);
+  border-inline-start-color: var(--accent-primary);
 }
 
 .tool-call-task-item[data-task-status="error"] {
-  border-left-color: var(--status-error);
+  border-inline-start-color: var(--status-error);
 }
 
 .tool-call-task-icon {
diff --git a/packages/ui/src/styles/panels/right-panel.css b/packages/ui/src/styles/panels/right-panel.css
index 6b9d2fcd..d2c08929 100644
--- a/packages/ui/src/styles/panels/right-panel.css
+++ b/packages/ui/src/styles/panels/right-panel.css
@@ -11,8 +11,8 @@
   content: '';
   position: absolute;
   bottom: -1px;
-  left: 0;
-  right: 0;
+  inset-inline-start: 0;
+  inset-inline-end: 0;
   height: 1px;
   background-color: var(--border-base);
   z-index: 0;
@@ -42,7 +42,7 @@
   border: 1px solid transparent;
   border-bottom: none;
   border-radius: 8px 8px 0 0;
-  margin-right: 2px;
+  margin-inline-end: 2px;
   z-index: 1;
 }
 
@@ -90,8 +90,8 @@
 .file-split-handle {
   cursor: col-resize;
   background-color: transparent;
-  border-left: 1px solid var(--border-base);
-  border-right: 1px solid var(--border-base);
+  border-inline-start: 1px solid var(--border-base);
+  border-inline-end: 1px solid var(--border-base);
   user-select: none;
   touch-action: none;
 }
@@ -148,7 +148,7 @@
   display: flex;
   flex-direction: column;
   background-color: var(--surface-secondary);
-  border-left: 1px solid var(--border-base);
+  border-inline-start: 1px solid var(--border-base);
   /* Monaco uses layered positioned elements; keep overlay well above it. */
   z-index: 200;
 }
@@ -459,7 +459,7 @@
 }
 
 .section-label {
-  margin-left: 2px;
+  margin-inline-start: 2px;
 }
 
 .section-info-icon {
diff --git a/packages/ui/src/styles/panels/session-layout.css b/packages/ui/src/styles/panels/session-layout.css
index f03cf6a7..9b0395ec 100644
--- a/packages/ui/src/styles/panels/session-layout.css
+++ b/packages/ui/src/styles/panels/session-layout.css
@@ -26,10 +26,10 @@
   position: absolute;
   top: 0;
   bottom: 0;
-  left: 0;
+  inset-inline-start: 0;
   width: min(90vw, 360px);
   max-width: 360px;
-  border-right: 1px solid var(--border-base);
+  border-inline-end: 1px solid var(--border-base);
   box-shadow: var(--folder-card-shadow);
   transform: translateX(0);
   transition: transform 0.25s ease, opacity 0.2s ease;
@@ -41,6 +41,9 @@
   opacity: 0;
   pointer-events: none;
 }
+[dir="rtl"] .session-sidebar-collapsed {
+  transform: translateX(100%);
+}
 
 .session-sidebar-backdrop {
   @apply absolute inset-0;
@@ -54,7 +57,7 @@
 .session-sidebar-menu-button--floating {
   position: absolute;
   top: 1rem;
-  left: 1rem;
+  inset-inline-start: 1rem;
   z-index: 20;
 }
 
@@ -128,7 +131,7 @@ session-sidebar-controls .selector-trigger-primary {
 .mobile-fullscreen-exit-wrapper {
   position: fixed;
   top: calc(env(safe-area-inset-top, 0px) + 12px);
-  right: calc(env(safe-area-inset-right, 0px) + 12px);
+  inset-inline-end: calc(env(safe-area-inset-right, 0px) + 12px);
   z-index: 1250;
   pointer-events: none;
 }
@@ -143,11 +146,11 @@ session-sidebar-controls .selector-trigger-primary {
 }
 
 .session-resize-handle--left {
-  right: 0;
+  inset-inline-end: 0;
 }
 
 .session-resize-handle--right {
-  left: 0;
+  inset-inline-start: 0;
 }
 
 .session-resize-handle:hover {
@@ -160,14 +163,20 @@ session-sidebar-controls .selector-trigger-primary {
 }
 
 .session-resize-handle--left::before {
-  right: 0;
+  inset-inline-end: 0;
   transform: translateX(50%);
 }
+[dir="rtl"] .session-resize-handle--left::before {
+  transform: translateX(-50%);
+}
 
 .session-resize-handle--right::before {
-  left: 0;
+  inset-inline-start: 0;
   transform: translateX(-50%);
 }
+[dir="rtl"] .session-resize-handle--right::before {
+  transform: translateX(50%);
+}
 
 .session-list-header {
   @apply border-b relative;
@@ -197,7 +206,7 @@ session-sidebar-controls .selector-trigger-primary {
 
 
 .session-item-base.session-item-child {
-  padding-left: 2.25rem;
+  padding-inline-start: 2.25rem;
   position: relative;
 }
 
@@ -206,7 +215,7 @@ session-sidebar-controls .selector-trigger-primary {
   position: absolute;
   top: 0;
   bottom: 0;
-  left: 1.125rem;
+  inset-inline-start: 1.125rem;
   width: 1px;
   background-color: var(--text-secondary);
   opacity: 0.95;
@@ -221,7 +230,7 @@ session-sidebar-controls .selector-trigger-primary {
   content: "";
   position: absolute;
   top: 50%;
-  left: 1.125rem;
+  inset-inline-start: 1.125rem;
   width: 0.875rem;
   height: 1px;
   background-color: var(--text-secondary);
@@ -231,11 +240,11 @@ session-sidebar-controls .selector-trigger-primary {
 }
 
 .session-item-base.session-item-border-user {
-  border-left: 4px solid var(--message-user-border);
+  border-inline-start: 4px solid var(--message-user-border);
 }
 
 .session-item-base.session-item-border-assistant {
-  border-left: 4px solid var(--message-assistant-border);
+  border-inline-start: 4px solid var(--message-assistant-border);
 }
 
 .session-item-expander {