修复消息气泡配色未跟设计稿核对过的问题：发出气泡改蓝底白字，接收气泡改浅灰，日期分隔去掉气泡背景

对照 docs/images/个人对话框（我的状态/对方的状态）.png：发出=蓝色实心+白字，接收=浅灰+深字，
与其余相关截图口径一致；旧配色（接收浅绿#c4e0a3、发出用页面同款off-white）不匹配任何参考图，
是尚未跟设计稿核对过的原始默认值。顺带修了一个自查时发现的新问题：已读回执图标复用的.blue
工具类和新的蓝色发出气泡背景是同一个色值，之前会变成看不见的勾选图标，改为不透明白色。

Co-Authored-By: Claude Sonnet 5 <noreply@anthropic.com>

css/base.css

@@ -133,15 +133,18 @@
   --clr-input-invalid-shadow: light-dark(#e5737340, #1a0c0c40);
   --clr-input-placeholder-text: var(--clr-text-placeholder);
 
-  /* Chat Bubbles */
+  /* Chat Bubbles -- docs/images/个人对话框（我的状态）.png 与 ...（对方的状态）.png：发出=蓝色实心+白字，
-  --clr-bubble-left-bg: light-dark(#c4e0a3, #3e5c1f);
+     收到=浅灰+深字，这两份参考图和之前所有相关截图口径一致；旧值（收到浅绿#c4e0a3、发出用页面同款
-  --clr-bubble-left-bg-flash: light-dark(#94a97c, #2c4517);
+     off-white）不匹配任何一张参考图，是尚未跟设计稿核对过的原始默认值，这次改成实际设计要求的配色。 */
-  --clr-bubble-right-bg: var(--clr-background-off-white);
+  --clr-bubble-left-bg: light-dark(#f0f0f0, #2c2c2e);
-  --clr-bubble-right-bg-flash: var(--clr-border-light);
+  --clr-bubble-left-bg-flash: light-dark(#d8d8d8, #3a3a3c);
+  --clr-bubble-right-bg: var(--clr-primary-accent);
+  --clr-bubble-right-bg-flash: var(--clr-primary-accent-hover);
   --clr-bubble-text: light-dark(#212121, #bbc);
+  --clr-bubble-right-text: #fff;
   --clr-bubble-meta-text: var(--clr-text-primary);
   --clr-bubble-meta-deleted-bg: var(--clr-primary-wash);
-  --clr-bubble-meta-date-bg: light-dark(rgba(255 255 255 / 80%), rgba(40 40 40 / 80%));
+  --clr-bubble-meta-date-bg: transparent;
   --clr-bubble-timestamp-text: light-dark(#777, #888);
   --clr-bubble-author-text: light-dark(#777, #666);
 
@@ -4620,6 +4623,7 @@ video {
 
 .right .bubble {
   background-color: var(--clr-bubble-right-bg);
+  color: var(--clr-bubble-right-text);
   margin-left: 1.75rem;
 }
 
@@ -4776,6 +4780,22 @@ Font from 3x to almost normal, from 1 to 5 emojis in a message */
   user-select: none;
 }
 
+/* --clr-bubble-timestamp-text is a mid-gray tuned for the light-gray received bubble; on the new
+   solid-blue sent bubble it reads as too low-contrast, so the sent side gets its own translucent
+   white instead of a second global token. */
+.right .bubble .timestamp {
+  color: rgba(255, 255, 255, 0.85);
+}
+
+/* deliveryMarker()'s "read" checkmark uses the .blue utility class (lib/utils.js), which resolves
+   to --clr-primary-accent -- the exact same blue this bubble's background now is. Left as-is, a
+   read receipt on your own message would render an invisible checkmark. Opaque white keeps it a
+   shade brighter than the translucent timestamp text next to it, so "read" still reads as distinct
+   from plain "sent". */
+.right .bubble .timestamp .blue {
+  color: #fff !important;
+}
+
 /* The name of the person who sent the message
  * (group chat only)
  */