Improve style

frontend/src/styles.css

@@ -320,15 +320,16 @@ button:disabled { opacity: 0.5; cursor: not-allowed; }
   height: 144px;
   border-radius: 0;
   overflow: hidden;
-  background: transparent;
+  background: #f5f7fb;
   box-shadow: none;
 }
 .avatar.speaking { animation: pulse 0.7s infinite alternate; }
 .avatar-image {
   width: 100%;
   height: 100%;
-  object-fit: cover;
+  object-fit: contain;
   display: block;
+  mix-blend-mode: multiply;
 }
 .avatar-caption { font-weight: 700; }
 .login-page {
@@ -513,7 +514,7 @@ button:disabled { opacity: 0.5; cursor: not-allowed; }
   flex-direction: column;
   gap: 0.4rem;
   padding: 0;
-  background: transparent;
+  background: #f5f7fb;
   color: #14213d;
   border: none;
 }
@@ -523,8 +524,8 @@ button:disabled { opacity: 0.5; cursor: not-allowed; }
   flex: 1 1 auto;
   object-fit: contain;
   border: 0;
-  border-radius: 0;
-  background: transparent;
+  border-radius: 30px;
+  background: #f5f7fb;
 }
 .lesson-bubble {
   min-height: 68px;
@@ -791,7 +792,7 @@ button:disabled { opacity: 0.5; cursor: not-allowed; }
     max-height: none;
     border-left: 0;
     border-right: 0;
-    border-radius: 0;
+    border-radius: 24px;
   }
 
   .lesson-composer {