Centered burger menu

frontend/src/App.tsx

@@ -22,8 +22,12 @@ export default function App() {
     <div className={`site ${open ? "sidebar-open" : ""}`}>
       {/* Top-left header (outside the card) */}
       <header className="site-header">
-        <button className="burger" aria-label="Menu" onClick={() => setOpen(v => !v)}>
-          ☰
+        <button className="burger" aria-label="メニュー" onClick={() => setOpen(v => !v)}>
+          <svg className="burger-icon" viewBox="0 0 24 24" width="22" height="22" aria-hidden="true">
+            <path d="M4 7h16M4 12h16M4 17h16"
+              stroke="currentColor" strokeWidth="2"
+              strokeLinecap="round" strokeLinejoin="round" fill="none" />
+          </svg>
         </button>
         <Link to="/" className="brand">Watch Party</Link>
       </header>

frontend/src/index.css

@@ -28,11 +28,29 @@ html, body, #root {
   display:flex; align-items:center; justify-content:space-between;
   margin-bottom: 12px;
 }
-.burger {
-  font-size:20px; line-height:1; padding:6px 10px; border-radius:8px;
-  background: rgba(255,255,255,0.08); border:1px solid rgba(255,255,255,0.15);
-  color: var(--text); cursor:pointer;
+/* Button container */
+.burger{
+  display:grid;                 /* centers SVG */
+  place-items:center;
+  width:40px; height:40px;      /* good touch target */
+  padding:0; line-height:0;     /* no baseline artifacts */
+  border-radius:12px;
+  color:var(--text);
+  background:rgba(255,255,255,.08);
+  border:1px solid rgba(255,255,255,.15);
+  cursor:pointer;
 }
+
+/* SVG itself */
+.burger-icon{
+  display:block;
+  shape-rendering:geometricPrecision;
+}
+
+/* polish */
+.burger:hover{ background:rgba(255,255,255,.12); }
+.burger:focus-visible{ outline:2px solid var(--accent); outline-offset:2px; }
+
 .brand { color: var(--text); text-decoration:none; font-weight:800; }
 .drawer {
   position:absolute; left:16px; top:56px; display:flex; flex-direction:column;
@@ -159,16 +177,6 @@ kbd {
   height: var(--header-h);
 }
 
-.burger {
-  font-size: 20px;
-  line-height: 1;
-  padding: 8px 10px;
-  border-radius: 10px;
-  color: var(--text);
-  background: rgba(255,255,255,0.08);
-  border: 1px solid rgba(255,255,255,0.15);
-  cursor: pointer;
-}
 .brand {
   font-weight: 900;
   color: var(--text);