当容器宽度大于设备宽度时，不会出现水平滚动条

Question

我已经在edx.org上开始了一个由Microsoft提供的高级CSS课程。在进行模块1时，我无法理解当容器宽度大于设备宽度时水平滚动条没有出现的原因。此外，为什么这些部分具有100％自动宽度。为什么容器宽度以像素为单位而不是％以使布局响应？

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/***************************
****************************
Reset Styles
****************************
***************************/


/*! normalize.css v4.1.1 | MIT License | github.com/necolas/normalize.css */


/**
 * 1. Change the default font family in all browsers (opinionated).
 * 2. Prevent adjustments of font size after orientation changes in IE and iOS.
 */

html {
  font-family: sans-serif;
  /* 1 */
  -ms-text-size-adjust: 100%;
  /* 2 */
  -webkit-text-size-adjust: 100%;
  /* 2 */
}


/**
 * Remove the margin in all browsers (opinionated).
 */

body {
  margin: 0;
}


/* HTML5 display definitions
   ========================================================================== */


/**
 * Add the correct display in IE 9-.
 * 1. Add the correct display in Edge, IE, and Firefox.
 * 2. Add the correct display in IE.
 */

article,
aside,
details,

/* 1 */

figcaption,
figure,
footer,
header,
main,

/* 2 */

menu,
nav,
section,
summary {
  /* 1 */
  display: block;
}


/**
 * Add the correct display in IE 9-.
 */

audio,
canvas,
progress,
video {
  display: inline-block;
}


/**
 * Add the correct display in iOS 4-7.
 */

audio:not([controls]) {
  display: none;
  height: 0;
}


/**
 * Add the correct vertical alignment in Chrome, Firefox, and Opera.
 */

progress {
  vertical-align: baseline;
}


/**
 * Add the correct display in IE 10-.
 * 1. Add the correct display in IE.
 */

template,

/* 1 */

[hidden] {
  display: none;
}


/* Links
   ========================================================================== */


/**
 * 1. Remove the gray background on active links in IE 10.
 * 2. Remove gaps in links underline in iOS 8+ and Safari 8+.
 */

a {
  background-color: transparent;
  /* 1 */
  -webkit-text-decoration-skip: objects;
  /* 2 */
}


/**
 * Remove the outline on focused links when they are also active or hovered
 * in all browsers (opinionated).
 */

a:active,
a:hover {
  outline-width: 0;
}


/* Text-level semantics
   ========================================================================== */


/**
 * 1. Remove the bottom border in Firefox 39-.
 * 2. Add the correct text decoration in Chrome, Edge, IE, Opera, and Safari.
 */

abbr[title] {
  border-bottom: none;
  /* 1 */
  text-decoration: underline;
  /* 2 */
  text-decoration: underline dotted;
  /* 2 */
}


/**
 * Prevent the duplicate application of `bolder` by the next rule in Safari 6.
 */

b,
strong {
  font-weight: inherit;
}


/**
 * Add the correct font weight in Chrome, Edge, and Safari.
 */

b,
strong {
  font-weight: bolder;
}


/**
 * Add the correct font style in Android 4.3-.
 */

dfn {
  font-style: italic;
}


/**
 * Correct the font size and margin on `h1` elements within `section` and
 * `article` contexts in Chrome, Firefox, and Safari.
 */

h1 {
  font-size: 2em;
  margin: 0.67em 0;
}


/**
 * Add the correct background and color in IE 9-.
 */

mark {
  background-color: #ff0;
  color: #000;
}


/**
 * Add the correct font size in all browsers.
 */

small {
  font-size: 80%;
}


/**
 * Prevent `sub` and `sup` elements from affecting the line height in
 * all browsers.
 */

sub,
sup {
  font-size: 75%;
  line-height: 0;
  position: relative;
  vertical-align: baseline;
}

sub {
  bottom: -0.25em;
}

sup {
  top: -0.5em;
}


/* Embedded content
   ========================================================================== */


/**
 * Remove the border on images inside links in IE 10-.
 */

img {
  border-style: none;
}


/**
 * Hide the overflow in IE.
 */

svg:not(:root) {
  overflow: hidden;
}


/* Grouping content
   ========================================================================== */


/**
 * 1. Correct the inheritance and scaling of font size in all browsers.
 * 2. Correct the odd `em` font sizing in all browsers.
 */

code,
kbd,
pre,
samp {
  font-family: monospace, monospace;
  /* 1 */
  font-size: 1em;
  /* 2 */
}


/**
 * Add the correct margin in IE 8.
 */

figure {
  margin: 1em 40px;
}


/**
 * 1. Add the correct box sizing in Firefox.
 * 2. Show the overflow in Edge and IE.
 */

hr {
  box-sizing: content-box;
  /* 1 */
  height: 0;
  /* 1 */
  overflow: visible;
  /* 2 */
}


/* Forms
   ========================================================================== */


/**
 * 1. Change font properties to `inherit` in all browsers (opinionated).
 * 2. Remove the margin in Firefox and Safari.
 */

button,
input,
select,
textarea {
  font: inherit;
  /* 1 */
  margin: 0;
  /* 2 */
}


/**
 * Restore the font weight unset by the previous rule.
 */

optgroup {
  font-weight: bold;
}


/**
 * Show the overflow in IE.
 * 1. Show the overflow in Edge.
 */

button,
input {
  /* 1 */
  overflow: visible;
}


/**
 * Remove the inheritance of text transform in Edge, Firefox, and IE.
 * 1. Remove the inheritance of text transform in Firefox.
 */

button,
select {
  /* 1 */
  text-transform: none;
}


/**
 * 1. Prevent a WebKit bug where (2) destroys native `audio` and `video`
 *    controls in Android 4.
 * 2. Correct the inability to style clickable types in iOS and Safari.
 */

button,
html [type="button"],

/* 1 */

[type="reset"],
[type="submit"] {
  -webkit-appearance: button;
  /* 2 */
}


/**
 * Remove the inner border and padding in Firefox.
 */

button::-moz-focus-inner,
[type="button"]::-moz-focus-inner,
[type="reset"]::-moz-focus-inner,
[type="submit"]::-moz-focus-inner {
  border-style: none;
  padding: 0;
}


/**
 * Restore the focus styles unset by the previous rule.
 */

button:-moz-focusring,
[type="button"]:-moz-focusring,
[type="reset"]:-moz-focusring,
[type="submit"]:-moz-focusring {
  outline: 1px dotted ButtonText;
}


/**
 * Change the border, margin, and padding in all browsers (opinionated).
 */

fieldset {
  border: 1px solid #c0c0c0;
  margin: 0 2px;
  padding: 0.35em 0.625em 0.75em;
}


/**
 * 1. Correct the text wrapping in Edge and IE.
 * 2. Correct the color inheritance from `fieldset` elements in IE.
 * 3. Remove the padding so developers are not caught out when they zero out
 *    `fieldset` elements in all browsers.
 */

legend {
  box-sizing: border-box;
  /* 1 */
  color: inherit;
  /* 2 */
  display: table;
  /* 1 */
  max-width: 100%;
  /* 1 */
  padding: 0;
  /* 3 */
  white-space: normal;
  /* 1 */
}


/**
 * Remove the default vertical scrollbar in IE.
 */

textarea {
  overflow: auto;
}


/**
 * 1. Add the correct box sizing in IE 10-.
 * 2. Remove the padding in IE 10-.
 */

[type="checkbox"],
[type="radio"] {
  box-sizing: border-box;
  /* 1 */
  padding: 0;
  /* 2 */
}


/**
 * Correct the cursor style of increment and decrement buttons in Chrome.
 */

[type="number"]::-webkit-inner-spin-button,
[type="number"]::-webkit-outer-spin-button {
  height: auto;
}


/**
 * 1. Correct the odd appearance in Chrome and Safari.
 * 2. Correct the outline style in Safari.
 */

[type="search"] {
  -webkit-appearance: textfield;
  /* 1 */
  outline-offset: -2px;
  /* 2 */
}


/**
 * Remove the inner padding and cancel buttons in Chrome and Safari on OS X.
 */

[type="search"]::-webkit-search-cancel-button,
[type="search"]::-webkit-search-decoration {
  -webkit-appearance: none;
}


/**
 * Correct the text style of placeholders in Chrome, Edge, and Safari.
 */

::-webkit-input-placeholder {
  color: inherit;
  opacity: 0.54;
}


/**
 * 1. Correct the inability to style clickable types in iOS and Safari.
 * 2. Change font properties to `inherit` in Safari.
 */

::-webkit-file-upload-button {
  -webkit-appearance: button;
  /* 1 */
  font: inherit;
  /* 2 */
}

html {
  box-sizing: border-box;
}

*,
*:before,
*:after {
  box-sizing: inherit;
}


/***************************
****************************
Base Styles
****************************
***************************/

body {
  color: #414042;
  font-family: Arial, Helvetica, sans-serif;
  font-weight: normal;
}

h1,
h2,
h3 {
  font-weight: bold;
}

a {
  color: #8dc63f;
  font-weight: bold;
}

a:hover {
  text-decoration: underline;
}


/***************************
****************************
Layout Styles
****************************
***************************/

.container {
  padding-left: 15px;
  padding-right: 15px;
  margin-right: auto;
  margin-left: auto;
  max-width: 1170px;
}

.row {
  margin-right: -15px;
  margin-left: -15px;
}

.row:after {
  content: "";
  display: table;
  clear: both;
}


/***************************
****************************
Module Styles
****************************
***************************/


/***************************
****************************
Theme Styles
****************************
***************************/

.background-primary {
  background: #F7941E;
  /*Orange*/
}

.background-secondary {
  background: #00AEEF;
  /*Blue*/
}

.background-tertiary {
  background: #8DC63F;
  /*Green*/
}

<!DOCTYPE html>
<html>

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>title</title>
  <link rel="stylesheet" href="stylesheet.css" type="text/css">
</head>

<body>
  <header class="background-primary">
    <div class="container">
      Header Content
    </div>
  </header>
  <main>
    <section class="background-secondary">
      <div class="container">
        Hero Primary Content
      </div>
    </section>
    <section>
      <div class="container">
        Image and Text Content
      </div>
    </section>
    <section>
      <div class="container">
        Featured Content
      </div>
    </section>
    <section class="background-primary">
      <div class="container">
        Testimonial Content
      </div>
    </section>
    <section class="background-secondary">
      <div class="container">Media Objects
      </div>
    </section>
    <section class="background-tertiary">
      <div class="container">
        More Content
      </div>
    </section>
  </main>
  <footer class="background-primary">
    <div class="container">
      Footer Content
    </div>
  </footer>
</body>

</html>

Answer 1

1. 由于没有溢出，因此没有出现水平滚动条。如果检查元素，您将看到section元素占据屏幕宽度的100％。

2. .container元素占据宽度的100％，因为它们是块级元素。这就是他们的行为方式。 请在此处阅读：https://developer.mozilla.org/en-US/docs/Web/HTML/Block-level_elements和https://developer.mozilla.org/en-US/docs/Web/HTML/Element/section

3. width元素没有被max-width: 1170px给出，它们被赋予{{1}}。这意味着他们将会响应＆＃34;高达1170px。有时您希望将应用/页面的内容保持在一定的宽度范围内 - 而不是根据设备屏幕的大小延伸。