Update dark theme and Center the elems

[Mattral]

Chat UI Styling Changes

Chat UI Container (chatui):

• Margin adjusted to center the entire chat UI horizontally.

Header Styles (chatui-header):

• Updated styles for dark mode, including border color, background color, and text color.

Chat Messages Container (chatui-chat):

• Updated styles for dark mode, including background color.

Message Bubble Styles (msg-bubble, .right-msg .msg-bubble, .left-msg .msg-bubble, .error-msg .msg-bubble, .init-msg .msg-bubble):

• Updated styles for dark mode, including background color and text color.

Input Area Styles (chatui-inputarea):

• Updated styles for dark mode, including border color and background color.

Input Field Styles (chatui-input):

• Updated styles for dark mode, including background color.

Reset Button Styles (chatui-reset-btn):

• Margin adjusted to center the reset button horizontally.
• Updated styles for dark mode, including background color, text color, and border color.

Send Button Styles (chatui-send-btn):

• Updated styles for dark mode, including background color.

Extra Control Styles (chatui-extra-control):

• Updated styles for dark mode, including background color.

Info Label Styles (chatui-info-label):

• Updated styles for dark mode, including text color.