* {
    margin: 0;
    padding: 0;
    box-sizing: border-box;
}

:root {
    --bg-color: #f5f5f5;
    --text-color: #333;
    --chat-bg: #fff;
    --user-msg-bg: #dcf8c6;
    --ai-msg-bg: #e5e5ea;
    --input-border: #ddd;
    --button-bg: #0078d4;
    --button-hover: #005a9e;
    --button-text: #fff;
}

.dark-mode {
    --bg-color: #1e1e1e;
    --text-color: #f0f0f0;
    --chat-bg: #2d2d2d;
    --user-msg-bg: #2b5278;
    --ai-msg-bg: #3a3b3c;
    --input-border: #444;
    --button-bg: #0078d4;
    --button-hover: #005a9e;
    --button-text: #fff;
}

body {
    font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, Oxygen, Ubuntu, Cantarell, 'Open Sans', 'Helvetica Neue', sans-serif;
    line-height: 1.6;
    color: var(--text-color);
    background-color: var(--bg-color);
    transition: background-color 0.3s ease, color 0.3s ease;
}

.container {
    max-width: 800px;
    margin: 0 auto;
    padding: 20px;
}

header {
    margin-bottom: 20px;
}

.header-content {
    display: flex;
    justify-content: space-between;
    align-items: center;
}

h1 {
    font-size: 2.5rem;
    color: var(--text-color);
    text-align: center;
    flex-grow: 1;
}

#theme-toggle {
    background: none;
    border: none;
    color: var(--text-color);
    font-size: 1.5rem;
    cursor: pointer;
}

#chat-container {
    background-color: var(--chat-bg);
    border-radius: 8px;
    box-shadow: 0 2px 10px rgba(0, 0, 0, 0.1);
    height: 400px;
    overflow-y: auto;
    padding: 20px;
    margin-bottom: 20px;
}

#input-container {
    display: flex;
    gap: 10px;
}

#user-input {
    flex-grow: 1;
    padding: 10px;
    border: 1px solid var(--input-border);
    border-radius: 4px;
    font-size: 1rem;
    resize: vertical;
    background-color: var(--chat-bg);
    color: var(--text-color);
}

#send-button, #clear-button {
    background-color: var(--button-bg);
    color: var(--button-text);
    border: none;
    border-radius: 4px;
    padding: 10px 20px;
    font-size: 1rem;
    cursor: pointer;
    transition: background-color 0.3s ease;
}

#send-button:hover, #clear-button:hover {
    background-color: var(--button-hover);
}

#send-button.ttsing {
    background-color: #999;
    cursor: not-allowed;
}

.message {
    margin-bottom: 15px;
    padding: 10px;
    border-radius: 8px;
    max-width: 80%;
    position: relative;
    animation: fadeIn 0.5s ease-out;
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(10px); }
    to { opacity: 1; transform: translateY(0); }
}

.user-message {
    background-color: var(--user-msg-bg);
    align-self: flex-end;
    margin-left: auto;
}

.ai-message {
    background-color: var(--ai-msg-bg);
    align-self: flex-start;
}

.message-time {
    font-size: 0.8rem;
    color: #888;
    position: absolute;
    bottom: -20px;
    right: 0;
}

.copy-button {
    position: absolute;
    top: 5px;
    right: 5px;
    background: none;
    border: none;
    cursor: pointer;
    font-size: 1rem;
    color: var(--text-color);
}

.copy-button:hover {
    color: var(--button-bg);
}

.placeholder {
    width: 1.5rem; /* 与主题切换按钮宽度相同 */
}