:root {
    --primary-color: #007aff;
    --bg-color: #f2f2f7;
    --card-bg: #ffffff;
    --text-color: #1d1d1f;
    --secondary-text: #86868b;
    --border-color: #d2d2d7;
}

body {
    margin: 0; 
    font-family: 'Inter', sans-serif;
    background: var(--bg); 
    color: var(--text);
    /* 修改以下部分 */
    display: flex; 
    flex-direction: column; /* 纵向排列 */
    align-items: center;    /* 水平居中 */
    justify-content: flex-start; /* 从顶部开始 */
    min-height: 100vh;
    padding: 0; /* 移除默认内边距，方便导航栏置顶 */
}

.container {
    width: 100%;
    max-width: 600px;
    background: var(--card-bg);
    padding: 30px;
    border-radius: 24px;
    box-shadow: 0 10px 40px rgba(0,0,0,0.08);
}

h2 { margin-top: 0; font-size: 20px; text-align: center; margin-bottom: 25px; }

.form-row { display: flex; gap: 15px; margin-bottom: 20px; }
.form-group { flex: 1; }
label { display: block; margin-bottom: 8px; font-size: 13px; font-weight: 500; color: var(--secondary-text); }

input, select {
    width: 100%;
    padding: 12px;
    border: 1px solid var(--border-color);
    border-radius: 12px;
    font-size: 15px;
    outline: none;
    box-sizing: border-box;
    background-color: #fff;
}

optgroup { font-style: normal; font-weight: bold; color: var(--primary-color); }

.result-card {
    background: #fbfbfd;
    border-radius: 18px;
    padding: 24px;
    text-align: center;
    border: 1px solid #efeff4;
    margin-bottom: 25px;
}

.rate-badge {
    display: inline-block;
    background: #e8f2ff;
    color: var(--primary-color);
    padding: 4px 14px;
    border-radius: 20px;
    font-size: 14px;
    font-weight: 600;
    margin-bottom: 10px;
}

.main-amount {
    font-size: 32px;
    font-weight: 700;
    color: var(--text-color);
    margin: 8px 0;
}

.time-picker { display: flex; gap: 8px; margin-bottom: 15px; }
.time-btn {
    flex: 1;
    padding: 8px 0;
    border: none;
    background: #eeeef0;
    border-radius: 10px;
    font-size: 13px;
    cursor: pointer;
    color: var(--secondary-text);
}

.time-btn.active {
    background: var(--primary-color);
    color: white;
    font-weight: 600;
}

.chart-container { height: 300px; position: relative; margin-top: 10px; }
#loading-overlay {
    position: absolute; top: 50%; left: 50%;
    transform: translate(-50%, -50%);
    font-size: 13px; color: var(--secondary-text);
    display: none; background: rgba(255,255,255,0.8);
    padding: 10px; border-radius: 8px; z-index: 10;
}