方法一

  • 左边设置宽度，右边设为flex即可
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<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
</head>

<body>
    <div class="left"></div>
    <div class="right"></div>
</body>

</html>

<style>
    body,
    html {
        height: 100%;
        width: 100%;
    }

    .left {
        width: 100px;
        height: 100%;
        background-color: red;
    }

    .right {
        flex: 1; // 填满空间
        background-color: blueviolet;
    }
</style>

方法二

  • 左侧固定宽度左浮动，右侧设margin-left等于左侧宽度，右侧宽度通过calc来计算，或者直接设为auto
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.left {
    width: 100px;
    height: 100%;
    float: left;
    background-color: red;
}

.right {
    // width: auto;
    width: calc(100% - 100px);
    margin-left: 100px;
    height: 100%;
    background-color: blueviolet;
}

方法三

  • 利用浮动+BFC
  • 左边设为浮动，右边触发BFC，BFC区域不会与浮动元素重叠
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.left {
    width: 100px;
    height: 100%;
    float: left;
    background-color: red;
}

.right {
    overflow: hidden;
    height: 100%;
    background-color: blueviolet;
}

方法四

  • 利用绝对定位
  • 父元素设为相对定位
  • 子元素设为left为0，设置宽度，右边元素left设为左边元素的宽度，right设为0即可
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body,
html {
    height: 100%;
    width: 100%;
    position: relative;
}

.left {
    position: absolute;
    width: 100px;
    height: 100%;
    left: 0;
    background-color: red;
}

.right {
    position: absolute;
    left: 100px;
    right: 0;
    width: auto;
    height: 100%;
    background-color: blueviolet;
}