/* --- 通用样式 & 变量 --- */
:root {
    --primary-color: #007bff; /* 主蓝色，用于按钮、高亮 */
    --accent-color: #28a745; /* 强调绿色，用于结果 */
    --warning-color: #dc3545; /* 警告红色，用于错误/购汇价 */
    --text-color: #333; /* 主要文字颜色 */
    --light-text-color: #777; /* 次要文字颜色 */
    --bg-light: #f8fbfd; /* 浅背景色 */
    --bg-gradient-start: #e0f2f7; /* 背景渐变开始 */
    --bg-gradient-end: #c1e4f2; /* 背景渐变结束 */
    --border-color: #e0e0e0; /* 边框颜色 */
    --shadow-light: rgba(0, 0, 0, 0.08); /* 轻微阴影 */
    --shadow-medium: rgba(0, 0, 0, 0.15); /* 中等阴影 */
    --shadow-heavy: rgba(0, 0, 0, 0.25); /* 较重阴影 */
    --border-radius-small: 8px;
    --border-radius-medium: 12px;
    --border-radius-large: 20px;
    --spacing-xs: 8px;
    --spacing-sm: 12px;
    --spacing-md: 20px;
    --spacing-lg: 30px;
    --swap-button-active-color: #495057; 
}

body {
    font-family: 'Noto Sans SC', 'Segoe UI', Tahoma, Geneva, Verdana, sans-serif;
    background: linear-gradient(135deg, var(--bg-gradient-start), var(--bg-gradient-end));
    display: flex;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    margin: 0;
    color: var(--text-color);
    padding: var(--spacing-md);
    box-sizing: border-box;
    overflow-x: hidden;
}

.container {
    background-color: #ffffff;
    padding: var(--spacing-lg) var(--spacing-md);
    border-radius: var(--border-radius-large);
    box-shadow: 0 15px 40px var(--shadow-medium);
    width: 100%;
    max-width: 550px;
    text-align: center;
    border: 1px solid var(--border-color);
    animation: fadeIn 0.8s ease-out;
    position: relative; 
    padding-bottom: 130px; 
}

@keyframes fadeIn {
    from { opacity: 0; transform: translateY(20px); }
    to { opacity: 1; transform: translateY(0); }
}

/* --- 头部标题 --- */
h1 {
    color: var(--text-color);
    margin-bottom: var(--spacing-lg);
    font-size: 2.2em;
    font-weight: 700;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: var(--spacing-sm);
}

/* payments icon for H1 (URL-encoded SVG, not Base64) */
.icon-earth { 
    display: inline-block;
    width: 32px;
    height: 32px;
    /* 新的 payments 图标 (URL 编码的 SVG) */
    background-image: url("data:image/svg+xml,%3Csvg%20xmlns%3D%22http%3A%2F%2Fwww.w3.org%2F2000%2Fsvg%22%20viewBox%3D%220%200%2024%2024%22%3E%3Cpath%20fill%3D%22currentColor%22%20d%3D%22M21%204H3c-1.11%200-2%20.89-2%202v12c0%201.11.89%202%202%202h18c1.11%200%202-.89%202-2V6c0-1.11-.89-2-2-2zm0%2014H3V6h18v12zM12%207c-2.76%200-5%202.24-5%205s2.24%205%205%205%205-2.24%205-5-2.24-5-5-5zm0%208c-1.66%200-3-1.34-3-3s1.34-3%203-3%203%201.34%203%203-1.34%203-3%203z%22%2F%3E%3C%2Fsvg%3E");
    background-size: contain;
    background-repeat: no-repeat;
    background-position: center;
    vertical-align: middle;
    /* 确保图标颜色是主蓝色，因为 SVG 中使用了 currentColor */
    color: var(--primary-color); 
}

/* --- 输入与选择组样式 --- */
.input-group, .select-group {
    margin-bottom: var(--spacing-md);
    text-align: left;
}

label {
    display: block;
    margin-bottom: var(--spacing-xs);
    font-weight: 600;
    color: var(--light-text-color);
    font-size: 0.95em;
}

input[type="number"] {
    width: 100%;
    padding: 14px 18px;
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-small);
    font-size: 1.15em;
    box-sizing: border-box;
    background-color: var(--bg-light);
    transition: border-color 0.3s, box-shadow 0.3s;
    -webkit-appearance: none;
    -moz-appearance: textfield;
}

input[type="number"]:focus {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 4px rgba(0, 123, 255, 0.2);
    outline: none;
}

/* --- 货币选择器布局 --- */
.currency-selectors {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-bottom: var(--spacing-lg);
    gap: var(--spacing-md);
}

.currency-selectors .select-group {
    flex: 1; 
    min-width: 0; 
    margin-bottom: 0;
}

/* --- 交换按钮样式 --- */
.swap-button {
    background-color: #6c757d;
    background-image: url("data:image/svg+xml,%3Csvg xmlns='http://www.w3.org/2000/svg' viewBox='0 0 24 24'%3E%3Cpath fill='%23FFFFFF' d='M7 16h10V8L21 12L17 16V10H7v6zm10-8H7V2L3 6L7 10V4h10v4z'/%3E%3C/svg%3E");
    background-size: 60%; 
    background-repeat: no-repeat;
    background-position: center;
    border-radius: 50%;
    cursor: pointer;
    width: 55px; 
    height: 55px;
    box-shadow: 0 5px 15px var(--shadow-light);
    transition: background-color 0.3s ease, transform 0.3s ease-in-out, box-shadow 0.3s ease;
    flex-shrink: 0;
}

.swap-button:hover {
    background-color: var(--primary-color);
    transform: rotate(360deg) scale(1.05);
    box-shadow: 0 8px 20px var(--shadow-light);
}
.swap-button:active {
    transform: scale(0.95);
    background-color: var(--swap-button-active-color); 
}

/* --- 结果显示区域 --- */
.results {
    background-color: #e6f7ff;
    border: 1px solid #b3e0ff;
    border-radius: var(--border-radius-medium);
    padding: var(--spacing-md) var(--spacing-lg);
    margin-top: var(--spacing-lg);
    text-align: left;
    line-height: 1.8;
}

.results p {
    margin: 0 0 var(--spacing-sm) 0;
    font-size: 1.2em;
    color: var(--accent-color);
    font-weight: 500;
    display: flex;
    justify-content: space-between;
    align-items: center;
    flex-wrap: wrap;
}

.results p:last-child {
    margin-bottom: 0;
}

.results span {
    font-weight: bold;
    color: var(--primary-color);
}

.buy-rate-info {
    font-size: 0.95em !important;
    color: var(--light-text-color) !important;
    margin-top: var(--spacing-sm) !important;
    border-top: 1px dashed #c0d4e0;
    padding-top: var(--spacing-sm);
}
.buy-rate-info span {
    color: var(--warning-color) !important;
}

/* --- 消息区域 (加载中 & 错误) --- */
.message-area {
    position: absolute; 
    bottom: 60px; 
    left: 50%;
    transform: translateX(-50%);
    width: calc(100% - 2 * var(--spacing-md));
    max-width: 400px;
    z-index: 10; 
    pointer-events: none; 
    opacity: 0; 
    visibility: hidden; 
    transition: opacity 0.3s ease, visibility 0.3s ease, transform 0.3s ease;
}

.message-area .loading,
.message-area .error {
    display: block; 
    padding: var(--spacing-sm) var(--spacing-md);
    border-radius: var(--border-radius-medium);
    font-weight: bold;
    text-align: center;
    box-shadow: 0 4px 10px var(--shadow-light);
    margin: 0;
}

.loading {
    color: var(--primary-color);
    background-color: #eaf6ff;
    border: 1px solid #b0e0ff;
}

.error {
    color: var(--warning-color);
    background-color: #ffe6e6;
    border: 1px solid #ffb3b3;
}

.message-area.is-visible {
    opacity: 1;
    visibility: visible;
    transform: translateX(-50%) translateY(-10px);
    pointer-events: auto; 
}
.message-area .loading:not(.is-active),
.message-area .error:not(.is-active) {
    display: none;
}


/* --- 底部说明文字 --- */
.update-time, .api-note {
    font-size: 0.85em;
    color: var(--light-text-color);
    line-height: 1.5;
    text-align: center;
}
.update-time {
    margin-top: var(--spacing-md); 
    margin-bottom: var(--spacing-xs); 
}
.api-note {
    margin-bottom: var(--spacing-sm); 
}


/* --- Select2 自定义样式 --- */
.select2-container {
    width: 100% !important;
    font-size: 1.15em;
}

.select2-container .select2-selection--single {
    height: 48px;
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-small);
    background-color: var(--bg-light);
    display: flex;
    align-items: center;
    transition: border-color 0.3s, box-shadow 0.3s;
}

.select2-container .select2-selection__rendered {
    line-height: normal;
    padding-left: 18px;
    padding-right: 40px;
    color: var(--text-color);
}

.select2-container--default .select2-selection--single .select2-selection__arrow {
    height: 46px;
    width: 30px;
    right: 5px;
    top: 1px;
}
.select2-container--default .select2-selection--single .select2-selection__arrow b {
    border-color: #888 transparent transparent transparent !important;
    border-width: 6px 4px 0 4px !important;
    margin-top: -3px !important;
}

.select2-container--default .select2-selection--single:focus-within,
.select2-container--default.select2-container--focus .select2-selection--single {
    border-color: var(--primary-color);
    box-shadow: 0 0 0 4px rgba(0, 123, 255, 0.2);
    outline: none;
}

.select2-dropdown {
    border: 1px solid var(--border-color);
    border-radius: var(--border-radius-small);
    box-shadow: 0 8px 20px var(--shadow-light);
    overflow: hidden;
}

.select2-search__field {
    padding: var(--spacing-sm) var(--spacing-md) !important;
    font-size: 1.05em !important;
    border-radius: var(--border-radius-small) !important;
    border: 1px solid var(--border-color) !important;
    box-shadow: none !important;
    margin: var(--spacing-sm);
    width: calc(100% - 2 * var(--spacing-sm)) !important;
    background-color: var(--bg-light);
}

.select2-results__option {
    padding: var(--spacing-sm) var(--spacing-md);
    font-size: 1em;
    color: var(--text-color);
    transition: background-color 0.2s ease;
}

.select2-results__option--highlighted {
    background-color: var(--primary-color) !important;
    color: white !important;
}

.select2-results__option[aria-selected=true] {
    background-color: #f0f8ff;
    color: var(--primary-color);
}

/* --- 响应式调整 (手机端优化) --- */
@media (max-width: 600px) {
    body {
        padding: var(--spacing-sm);
    }
    .container {
        padding: var(--spacing-md) var(--spacing-sm);
        border-radius: var(--border-radius-medium);
        box-shadow: 0 8px 20px rgba(0, 0, 0, 0.12);
        padding-bottom: 120px; 
    }
    h1 {
        font-size: 1.8em;
        margin-bottom: var(--spacing-md);
        gap: var(--spacing-xs);
    }
    .icon-earth {
        width: 28px;
        height: 28px;
    }
    input[type="number"] {
        padding: 12px 15px;
        font-size: 1.05em;
    }
    .currency-selectors {
        flex-direction: column;
        gap: var(--spacing-md);
        margin-bottom: var(--spacing-md);
    }
    .select-group {
        width: 100%;
    }
    label {
        width: auto;
    }
    .swap-button {
        width: 48px;
        height: 48px;
        font-size: 1.3em;
        margin: 5px auto;
    }
    .select2-container .select2-selection--single {
        height: 44px;
    }
    .select2-container .select2-selection__rendered {
        padding-left: 15px;
    }
    .select2-container--default .select2-selection--single .select2-selection__arrow {
        height: 42px;
    }
    .results {
        padding: var(--spacing-md);
        border-radius: var(--border-radius-small);
    }
    .results p {
        font-size: 1.1em;
        flex-direction: column;
        align-items: flex-start;
    }
    .results p span {
        margin-top: 5px;
        display: block;
        font-size: 1em;
    }
    .buy-rate-info {
        font-size: 0.9em !important;
        padding-top: 10px;
    }
    .update-time, .api-note {
        font-size: 0.8em;
        margin-top: var(--spacing-md);
    }
    .message-area {
        width: calc(100% - 2 * var(--spacing-sm));
        bottom: 50px; 
    }
}