body {
    display: flex;
    flex-direction: column;
    justify-content: center;
    align-items: center;
    min-height: 100vh;
    background-color: #1a1a1a; /* 暗黑背景 */
    margin: 0;
    padding: 20px;
    box-sizing: border-box;
}

.calculator {
    width: 320px;
    height: 580px;
    background-color: #000;
    border-radius: 25px;
    padding: 20px;
    box-shadow: 0 4px 20px rgba(0, 0, 0, 0.5);
}

.display-container {
    width: 100%;
    height: 170px; /* 固定高度：2条历史记录(60px) + display区域(60px) + padding(40px) + 间距(10px) */
    background-color: #333;
    border-radius: 15px;
    padding: 20px;
    box-sizing: border-box;
    margin-bottom: 20px;
    overflow: hidden;
    position: relative;
    display: flex;
    flex-direction: column;
    justify-content: flex-end; /* 内容靠底部对齐 */
}

.history {
    width: 100%;
    height: 60px; /* 固定高度：2条历史记录 */
    margin-bottom: 10px;
    overflow: hidden;
    display: flex;
    flex-direction: column;
    justify-content: flex-end;
}

.history-item {
    width: 100%;
    height: 30px;
    color: #888;
    font-size: 1em;
    text-align: right;
    padding: 5px 0;
    box-sizing: border-box;
    overflow: hidden;
    text-overflow: ellipsis;
    white-space: nowrap;
    opacity: 0;
    transform: translateY(20px);
    transition: opacity 0.3s ease, transform 0.3s ease;
}

.history-item:not(:empty) {
    opacity: 1;
    transform: translateY(0);
}

.history-item:empty {
    display: none;
}

.display {
    width: 100%;
    height: 60px; /* 固定高度 */
    color: white;
    font-size: 2.5em;
    text-align: right;
    padding: 0;
    box-sizing: border-box;
    display: flex;
    align-items: center;
    justify-content: flex-end;
    line-height: 1;
}

.button {
    width: 60px;
    height: 60px;
    margin: 10px;
    border: none;
    border-radius: 50%;
    font-size: 1.5em;
    color: white;
    transition: background-color 0.2s;
}

.button:active {
    background-color: #555;
}

.button.orange {
    background-color: #f79e1b;
}

.button.gray {
    background-color: #a5a5a5;
}

.button.dark-gray {
    background-color: #333;
}

/* 数字 0 按钮特殊样式：上下边为水平线，左右为圆弧 */
.button.zero {
    width: 140px; /* 两个按钮的宽度加上间距 */
    border-radius: 30px; /* 左右圆弧 */
    text-align: center; /* 文本居中 */
    padding-left: 0; /* 移除左侧内边距 */
}

.row {
    display: flex;
    justify-content: space-between;
}

footer {
    margin-top: 30px;
    padding: 20px 0;
    text-align: center;
}

footer a {
    opacity: 0.6;
    transition: opacity 0.2s;
}

footer a:hover {
    opacity: 0.8;
}

footer img {
    filter: grayscale(100%) brightness(3) invert(1); /* 浅色徽标：灰度+高亮度+反色 */
    transition: filter 0.2s;
}

footer a:hover img {
    filter: grayscale(80%) brightness(1.2) invert(1); /* 悬停时恢复彩色 */
}