/* --- 1. 全局重置与基础设定 --- */
:root {
    --ease-out-quart: cubic-bezier(0.25, 1, 0.5, 1);
    --font-family-system: system-ui, -apple-system, BlinkMacSystemFont, 'Segoe UI', Roboto, 'Helvetica Neue', Arial, sans-serif;

    /* 明亮主题颜色变量 */
    --bg-color-light: #f5f5f7;
    --card-bg-light: rgba(255, 255, 255, 0.6);
    --text-color-primary-light: #1d1d1f;
    --text-color-secondary-light: #6e6e73;
    --border-color-light: rgba(0, 0, 0, 0.1);
    --shadow-color-light: rgba(0, 0, 0, 0.05);
    --accent-color-light: #007aff;
    --textarea-bg-light: rgba(255, 255, 255, 0.5);

    /* 黑暗主题颜色变量 */
    --bg-color-dark: #161617;
    --card-bg-dark: rgba(29, 29, 31, 0.7);
    --text-color-primary-dark: #f5f5f7;
    --text-color-secondary-dark: #a1a1a6;
    --border-color-dark: rgba(255, 255, 255, 0.15);
    --shadow-color-dark: rgba(0, 0, 0, 0.2);
    --accent-color-dark: #0a84ff;
    --textarea-bg-dark: rgba(29, 29, 31, 0.5);
}

html {
    /* 动态主题切换 */
    --bg-color: var(--bg-color-light);
    --card-bg: var(--card-bg-light);
    --text-color-primary: var(--text-color-primary-light);
    --text-color-secondary: var(--text-color-secondary-light);
    --border-color: var(--border-color-light);
    --shadow-color: var(--shadow-color-light);
    --accent-color: var(--accent-color-light);
    --textarea-bg: var(--textarea-bg-light);
}

html[data-theme='dark'] {
    --bg-color: var(--bg-color-dark);
    --card-bg: var(--card-bg-dark);
    --text-color-primary: var(--text-color-primary-dark);
    --text-color-secondary: var(--text-color-secondary-dark);
    --border-color: var(--border-color-dark);
    --shadow-color: var(--shadow-color-dark);
    --accent-color: var(--accent-color-dark);
    --textarea-bg: var(--textarea-bg-dark);
}

body {
    margin: 0;
    font-family: var(--font-family-system);
    background-color: var(--bg-color);
    color: var(--text-color-primary);
    transition: background-color 0.4s var(--ease-out-quart), color 0.4s var(--ease-out-quart);
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
    overflow-x: hidden;
    position: relative;
}

/* --- 2. 动态背景 --- */
body::before {
    content: '';
    position: fixed;
    top: 0; left: 0;
    width: 100vw; height: 100vh;
    background: linear-gradient(45deg, #007aff, #5856d6, #ff2d55, #ff9500);
    background-size: 400% 400%;
    animation: gradient-animation 15s ease infinite;
    z-index: -1;
    opacity: 0.15;
}

@keyframes gradient-animation {
    0% { background-position: 0% 50%; }
    50% { background-position: 100% 50%; }
    100% { background-position: 0% 50%; }
}

/* --- 3. 布局与容器 --- */
.container {
    max-width: 1200px;
    margin: 0 auto;
    padding: 4rem 2rem;
}

.converter-grid {
    display: grid;
    grid-template-columns: 1fr 1fr;
    gap: 2rem;
}

/* --- 4. 组件样式 --- */
.card {
    background-color: var(--card-bg);
    backdrop-filter: blur(20px) saturate(180%);
    -webkit-backdrop-filter: blur(20px) saturate(180%);
    border: 1px solid var(--border-color);
    border-radius: 20px;
    padding: 2.5rem;
    box-shadow: 0 8px 32px 0 var(--shadow-color);
    transition: background-color 0.4s var(--ease-out-quart), border-color 0.4s var(--ease-out-quart);
}

.header {
    text-align: center;
    margin-bottom: 4rem;
}

h1 {
    font-size: 3rem;
    font-weight: 700;
    letter-spacing: -0.02em;
    margin: 0;
}

.subtitle {
    font-size: 1.25rem;
    color: var(--text-color-secondary);
    margin-top: 0.5rem;
    max-width: 600px;
    margin-left: auto;
    margin-right: auto;
}

label {
    display: block;
    font-size: 1.1rem;
    font-weight: 600;
    margin-bottom: 1rem;
}

textarea {
    width: 100%;
    min-height: 400px;
    padding: 1rem;
    box-sizing: border-box;
    border: 1px solid transparent;
    border-radius: 12px;
    background-color: var(--textarea-bg);
    color: var(--text-color-primary);
    font-family: 'SF Mono', 'Menlo', 'Courier New', monospace;
    font-size: 0.9rem;
    resize: vertical;
    outline: none;
    transition: all 0.3s var(--ease-out-quart);
}

textarea:focus {
    border-color: var(--accent-color);
    box-shadow: 0 0 0 4px color-mix(in srgb, var(--accent-color) 20%, transparent);
}

textarea::placeholder {
    color: var(--text-color-secondary);
    opacity: 0.7;
}

/* --- 5. 主题切换按钮 --- */
#theme-toggle {
    position: fixed;
    top: 2rem;
    right: 2rem;
    width: 44px;
    height: 44px;
    border-radius: 50%;
    border: 1px solid var(--border-color);
    background-color: var(--card-bg);
    backdrop-filter: blur(10px);
    -webkit-backdrop-filter: blur(10px);
    cursor: pointer;
    outline: none;
    display: flex;
    justify-content: center;
    align-items: center;
    transition: all 0.3s var(--ease-out-quart);
    z-index: 100;
    font-size: 1.2rem;
}
#theme-toggle:hover {
    transform: scale(1.1) rotate(15deg);
}

/* --- 6. 响应式设计 --- */
@media (max-width: 768px) {
    .container {
        padding: 2rem 1rem;
    }
    .converter-grid {
        grid-template-columns: 1fr;
    }
    h1 {
        font-size: 2.5rem;
    }
    .subtitle {
        font-size: 1rem;
    }
    #theme-toggle {
        top: 1rem;
        right: 1rem;
    }
}