/* 计算器前端样式（深色标准布局，与参考图一致） */
* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
  -webkit-user-select: none;
  user-select: none;
}

body {
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #17181a;
  font-family: "Segoe UI", "Microsoft YaHei", system-ui, sans-serif;
}

.calculator {
  width: 420px;
  max-width: 96vw;
  background: #202124;
  border-radius: 14px;
  padding: 18px 14px 14px;
  box-shadow: 0 12px 40px rgba(0, 0, 0, 0.5);
}

/* ---------- 顶部工具条 ---------- */
.toolbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 10px 10px;
}

.toolbar-title {
  color: #9aa0a6;
  font-size: 14px;
  font-weight: 600;
}

.hist-btn {
  border: none;
  border-radius: 6px;
  padding: 5px 12px;
  font-size: 13px;
  font-weight: 600;
  color: #ffffff;
  background: #3c4043;
  cursor: pointer;
  transition: background-color 0.12s ease;
}

.hist-btn:hover { background: #4a4e52; }
.hist-btn:active { filter: brightness(0.9); }

/* ---------- 历史面板 ---------- */
.hist-panel {
  background: #2a2d31;
  border-radius: 10px;
  margin: 0 0 8px;
  overflow: hidden;
  max-height: 260px;
  display: flex;
  flex-direction: column;
}

.hist-panel.hidden { display: none; }

.hist-head {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 10px 12px;
  border-bottom: 1px solid #3c4043;
}

.hist-title {
  color: #ffffff;
  font-size: 14px;
  font-weight: 600;
}

.hist-actions { display: flex; gap: 6px; }

.hist-action {
  border: none;
  border-radius: 5px;
  padding: 4px 10px;
  font-size: 12px;
  font-weight: 600;
  color: #ffffff;
  background: #5f6368;
  cursor: pointer;
  transition: background-color 0.12s ease;
}

.hist-action:hover { background: #6d7278; }
.hist-action:active { filter: brightness(0.9); }

.hist-list {
  overflow-y: auto;
  padding: 4px 8px;
  list-style: none;
}

.hist-empty {
  color: #9aa0a6;
  font-size: 13px;
  text-align: center;
  padding: 22px 0;
}

.hist-item {
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 7px 8px;
  border-radius: 6px;
  cursor: pointer;
}

.hist-item:hover { background: #363a40; }

.hist-main {
  flex: 1;
  min-width: 0;
  display: flex;
  align-items: baseline;
  gap: 6px;
  font-size: 14px;
}

.hist-expr {
  color: #9aa0a6;
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
}

.hist-eq { color: #5f6368; }

.hist-result {
  color: #ffffff;
  font-weight: 600;
  white-space: nowrap;
}

.hist-time {
  color: #6d7278;
  font-size: 11px;
  white-space: nowrap;
}

.hist-del {
  border: none;
  background: none;
  color: #9aa0a6;
  font-size: 16px;
  line-height: 1;
  cursor: pointer;
  padding: 2px 6px;
  border-radius: 4px;
}

.hist-del:hover { color: #ff8a80; background: #3c4043; }

/* ---------- 显示区 ---------- */
.display {
  background: #202124;
  padding: 8px 10px 14px;
  margin-bottom: 8px;
}

/* 表达式输入框 */
.expr-input {
  width: 100%;
  border: none;
  outline: none;
  background: transparent;
  color: #9aa0a6;
  font-size: 18px;
  font-family: "Segoe UI", "Microsoft YaHei", system-ui, sans-serif;
  text-align: right;
  padding: 2px 0 6px;
  caret-color: #1a73e8;
}

.expr-input::placeholder { color: #5f6368; }

.display-top {
  display: flex;
  justify-content: space-between;
  min-height: 22px;
}

.mem {
  color: #fbbc04;
  font-size: 14px;
  font-weight: 600;
}

.expr {
  color: #9aa0a6;
  font-size: 14px;
  white-space: nowrap;
  overflow: hidden;
}

.main {
  text-align: right;
  font-size: 42px;
  font-weight: 700;
  color: #ffffff;
  line-height: 1.15;
  overflow: hidden;
  white-space: nowrap;
  text-overflow: ellipsis;
  min-height: 50px;
}

.main.error {
  color: #ff8a80;
  font-size: 22px;
  line-height: 2.3;
}

/* ---------- 按键区 ---------- */
.keys {
  display: grid;
  grid-template-columns: repeat(5, 1fr);
  gap: 6px;
}

.key {
  height: 56px;
  border: none;
  border-radius: 8px;
  font-size: 19px;
  font-weight: 600;
  color: #ffffff;
  cursor: pointer;
  transition: background-color 0.12s ease;
}

.key.ghost {
  visibility: hidden;
  pointer-events: none;
}

.key.func { background: #5f6368; }
.key.digit { background: #3c4043; }
.key.op { background: #4d5a6d; }
.key.eq { background: #1a73e8; }

.key:hover { filter: brightness(1.18); }
.key:active { filter: brightness(0.9); }

.key.eq {
  grid-column: 1 / -1;
  height: 64px;
  font-size: 26px;
}

/* 小屏适配 */
@media (max-width: 460px) {
  .calculator { width: 100%; border-radius: 0; }
  .key { height: 52px; }
}