feat(select): implement custom Select component with dropdown functionality

src/components/ui/Select.module.scss

@@ -0,0 +1,107 @@
+@use '../../styles/mixins' as *;
+
+.wrap {
+  position: relative;
+  display: inline-flex;
+  align-items: center;
+  width: 100%;
+}
+
+.trigger {
+  display: inline-flex;
+  align-items: center;
+  justify-content: space-between;
+  gap: 8px;
+  width: 100%;
+  height: 40px;
+  padding: 0 12px;
+  border: 1px solid var(--border-color);
+  border-radius: $radius-md;
+  background-color: var(--bg-primary);
+  box-shadow: var(--shadow);
+  color: var(--text-primary);
+  font-size: 13px;
+  font-weight: 500;
+  cursor: pointer;
+  appearance: none;
+  text-align: left;
+  box-sizing: border-box;
+
+  &:hover {
+    border-color: var(--border-hover);
+  }
+
+  &:focus {
+    outline: none;
+    box-shadow: var(--shadow), 0 0 0 3px rgba($primary-color, 0.18);
+  }
+
+  &[aria-expanded='true'] {
+    border-color: var(--primary-color);
+    box-shadow: var(--shadow), 0 0 0 3px rgba($primary-color, 0.18);
+  }
+}
+
+.triggerText {
+  overflow: hidden;
+  text-overflow: ellipsis;
+  white-space: nowrap;
+}
+
+.placeholder {
+  color: var(--text-tertiary);
+}
+
+.triggerIcon {
+  display: inline-flex;
+  color: var(--text-secondary);
+  flex-shrink: 0;
+  transition: transform 0.2s ease;
+
+  [aria-expanded='true'] > & {
+    transform: rotate(180deg);
+  }
+}
+
+.dropdown {
+  position: absolute;
+  top: calc(100% + 6px);
+  left: 0;
+  right: 0;
+  z-index: 1000;
+  background: var(--bg-primary);
+  border: 1px solid var(--border-color);
+  border-radius: $radius-lg;
+  padding: 6px;
+  box-shadow: var(--shadow-lg);
+  display: flex;
+  flex-direction: column;
+  gap: 4px;
+  max-height: 240px;
+  overflow-y: auto;
+  overscroll-behavior: contain;
+}
+
+.option {
+  padding: 8px 12px;
+  border-radius: $radius-md;
+  border: 1px solid transparent;
+  background: transparent;
+  color: var(--text-primary);
+  cursor: pointer;
+  text-align: left;
+  font-size: 13px;
+  font-weight: 500;
+  transition: background-color 0.15s ease, border-color 0.15s ease;
+  flex-shrink: 0;
+
+  &:hover {
+    background: var(--bg-secondary);
+  }
+}
+
+.optionActive {
+  border-color: rgba($primary-color, 0.5);
+  background: rgba($primary-color, 0.1);
+  font-weight: 600;
+}

src/components/ui/Select.tsx

@@ -0,0 +1,75 @@
+import { useState, useEffect, useRef } from 'react';
+import { IconChevronDown } from './icons';
+import styles from './Select.module.scss';
+
+export interface SelectOption {
+  value: string;
+  label: string;
+}
+
+interface SelectProps {
+  value: string;
+  options: SelectOption[];
+  onChange: (value: string) => void;
+  placeholder?: string;
+  className?: string;
+}
+
+export function Select({ value, options, onChange, placeholder, className }: SelectProps) {
+  const [open, setOpen] = useState(false);
+  const wrapRef = useRef<HTMLDivElement | null>(null);
+
+  useEffect(() => {
+    if (!open) return;
+    const handleClickOutside = (event: MouseEvent) => {
+      if (!wrapRef.current?.contains(event.target as Node)) setOpen(false);
+    };
+    document.addEventListener('mousedown', handleClickOutside);
+    return () => document.removeEventListener('mousedown', handleClickOutside);
+  }, [open]);
+
+  const selected = options.find((o) => o.value === value);
+  const displayText = selected?.label ?? placeholder ?? '';
+  const isPlaceholder = !selected && placeholder;
+
+  return (
+    <div className={`${styles.wrap} ${className ?? ''}`} ref={wrapRef}>
+      <button
+        type="button"
+        className={styles.trigger}
+        onClick={() => setOpen((prev) => !prev)}
+        aria-haspopup="listbox"
+        aria-expanded={open}
+      >
+        <span className={`${styles.triggerText} ${isPlaceholder ? styles.placeholder : ''}`}>
+          {displayText}
+        </span>
+        <span className={styles.triggerIcon} aria-hidden="true">
+          <IconChevronDown size={14} />
+        </span>
+      </button>
+      {open && (
+        <div className={styles.dropdown} role="listbox">
+          {options.map((opt) => {
+            const active = opt.value === value;
+            return (
+              <button
+                key={opt.value}
+                type="button"
+                role="option"
+                aria-selected={active}
+                className={`${styles.option} ${active ? styles.optionActive : ''}`}
+                onClick={() => {
+                  onChange(opt.value);
+                  setOpen(false);
+                }}
+              >
+                {opt.label}
+              </button>
+            );
+          })}
+        </div>
+      )}
+    </div>
+  );
+}

src/components/usage/ChartLineSelector.tsx

@@ -1,6 +1,8 @@
+import { useMemo } from 'react';
 import { useTranslation } from 'react-i18next';
 import { Card } from '@/components/ui/Card';
 import { Button } from '@/components/ui/Button';
+import { Select } from '@/components/ui/Select';
 import styles from '@/pages/UsagePage.module.scss';
 
 export interface ChartLineSelectorProps {
@@ -41,6 +43,14 @@ export function ChartLineSelector({
     onChange(newLines);
   };
 
+  const options = useMemo(
+    () => [
+      { value: 'all', label: t('usage_stats.chart_line_all') },
+      ...modelNames.map((name) => ({ value: name, label: name }))
+    ],
+    [modelNames, t]
+  );
+
   return (
     <Card
       title={t('usage_stats.chart_line_actions_label')}
@@ -66,18 +76,11 @@ export function ChartLineSelector({
             <span className={styles.chartLineLabel}>
               {t(`usage_stats.chart_line_label_${index + 1}`)}
             </span>
-            <select
+            <Select
               value={line}
-              onChange={(e) => handleChange(index, e.target.value)}
-              className={styles.select}
-            >
-              <option value="all">{t('usage_stats.chart_line_all')}</option>
-              {modelNames.map((name) => (
-                <option key={name} value={name}>
-                  {name}
-                </option>
-              ))}
-            </select>
+              options={options}
+              onChange={(value) => handleChange(index, value)}
+            />
             {chartLines.length > 1 && (
               <Button variant="danger" size="sm" onClick={() => handleRemove(index)}>
                 {t('usage_stats.chart_line_delete')}

src/components/usage/CredentialStatsCard.tsx

@@ -277,10 +277,11 @@ export function CredentialStatsCard({
   }, [usage, geminiKeys, claudeConfigs, codexConfigs, vertexConfigs, openaiProviders, authFileMap]);
 
   return (
-    <Card title={t('usage_stats.credential_stats')}>
+    <Card title={t('usage_stats.credential_stats')} className={styles.detailsFixedCard}>
       {loading ? (
         <div className={styles.hint}>{t('common.loading')}</div>
       ) : rows.length > 0 ? (
+        <div className={styles.detailsScroll}>
         <div className={styles.tableWrapper}>
           <table className={styles.table}>
             <thead>
@@ -326,6 +327,7 @@ export function CredentialStatsCard({
             </tbody>
           </table>
         </div>
+        </div>
       ) : (
         <div className={styles.hint}>{t('usage_stats.no_data')}</div>
       )}

src/components/usage/PriceSettingsCard.tsx

@@ -1,8 +1,9 @@
-import { useState } from 'react';
+import { useState, useMemo } from 'react';
 import { useTranslation } from 'react-i18next';
 import { Card } from '@/components/ui/Card';
 import { Button } from '@/components/ui/Button';
 import { Input } from '@/components/ui/Input';
+import { Select } from '@/components/ui/Select';
 import type { ModelPrice } from '@/utils/usage';
 import styles from '@/pages/UsagePage.module.scss';
 
@@ -65,6 +66,14 @@ export function PriceSettingsCard({
     }
   };
 
+  const options = useMemo(
+    () => [
+      { value: '', label: t('usage_stats.model_price_select_placeholder') },
+      ...modelNames.map((name) => ({ value: name, label: name }))
+    ],
+    [modelNames, t]
+  );
+
   return (
     <Card title={t('usage_stats.model_price_settings')}>
       <div className={styles.pricingSection}>
@@ -73,18 +82,12 @@ export function PriceSettingsCard({
           <div className={styles.formRow}>
             <div className={styles.formField}>
               <label>{t('usage_stats.model_name')}</label>
-              <select
+              <Select
                 value={selectedModel}
-                onChange={(e) => handleModelSelect(e.target.value)}
-                className={styles.select}
-              >
-                <option value="">{t('usage_stats.model_price_select_placeholder')}</option>
-                {modelNames.map((name) => (
-                  <option key={name} value={name}>
-                    {name}
-                  </option>
-                ))}
-              </select>
+                options={options}
+                onChange={handleModelSelect}
+                placeholder={t('usage_stats.model_price_select_placeholder')}
+              />
             </div>
             <div className={styles.formField}>
               <label>{t('usage_stats.model_price_prompt')} ($/1M)</label>

src/pages/UsagePage.module.scss

@@ -741,24 +741,6 @@
   }
 }
 
-.select {
-  padding: 10px 12px;
-  border: 1px solid var(--border-color);
-  border-radius: $radius-md;
-  background-color: var(--bg-primary);
-  color: var(--text-primary);
-  font-size: 14px;
-  cursor: pointer;
-  height: 40px;
-  box-sizing: border-box;
-
-  &:focus {
-    outline: none;
-    border-color: var(--primary-color);
-    box-shadow: 0 0 0 3px rgba($primary-color, 0.18);
-  }
-}
-
 .pricesList {
   display: flex;
   flex-direction: column;