说明：本文对Chrome Developer Tools系列翻译文章的一篇

原文见https://developers.google.com/chrome-developer-tools/docs/elements-styles

Chrome Developer Tools: Element Styles

This tutorial covers editing CSS styles using various DevTools aids.

这个教程讲解了通过开发工具编辑CSS样式。

Note: If you are a Web Developer and want to get the latest version of Developer Tools, you should use the Google Chrome release from the Developer Channel.

注意：如果你是一个Web开发者，想要获得最新的开发工具，请从 Developer Channel里获取Google Chrome 发行版。

Contents

1. Computed Style Pane
2. Styles Pane
   1. Viewing Styles
   2. Editing Styles
   3. Adding New Rules and Properties
3. Metrics Pane
4. Persisting Changes

Computed Style Pane

计算样式窗格

• Invoke context menu on THIS (Inspect Me) element or hit Control-Shift-C to enter the Inspect Element mode and click on it. Alternatively, if you have DevTools open, click the Magnifier  button at the bottom of the Elements panel to point-click the element in the page.

• You will see several panes on the right-hand side of the panel. If the Computed Style pane is collapsed, expand it by clicking its header. The pane displays all the final values for CSS properties computed by the browser for the currently selected DOM node.

• For every property specified by more than one rule, the pane displays a computed trace, which is a stack of selectors applicable to the node and specifying the property value. Since rule selectors have different specificities, all but the top-most one will be “cancelled out” in the trace, which is denoted by a strike-through type.

• Whenever possible, a computed trace element will contain a link to the source code fragment that defines the respective rule.

• The pane contains only properties from rules that are directly applicable to the selected element. In order to additionally display inherited properties, enable the Show inherited checkbox. Such properties will be displayed in a dimmed font.

Styles Pane

• For the currently selected DOM node, this pane displays all the styles applicable to this node. Styles with gray background are read-only, the rest are editable.

• Invoke the DevTools inspector on THIS element as mentioned above.

Viewing Styles

• The styles are displayed as closely to the original declaration as possible. Some properties can have exclamation marks () next to their names. This means that the property name and/or value is not understood by the browser, so the property is ignored (as per the CSS specification).

• Note: A style declaration may contain several properties with the same name. Only the last one takes effect, canceling the preceding ones. Those will be struck out, like overridden properties.

• If a property value (say, background-image) contains a URL that has been loaded, you can click it to navigate to the corresponding resource in the Resources panel.

• CSS color values are accompanied by a swatch filled with the respective color. You can click the swatch to cycle through all color formats available for the corresponding property, or use the Gear menu options to set the format for all color values, for which the format has not been set by clicking on the color swatch. The As Authored option formats color values in the way they are written in the CSS code.

• Pseudo element styles, such as ::before, ::after, and many more -webkit-* ones, are also exposed in the Styles pane, along with the rules inherited from ancestor elements.

Editing Styles

• Double-click the worder property name, and type in bo instead. A valid border property name will be automatically suggested.

• Hit Down several times to reach the border-color suggestion, and press Enter or Tab to accept it and jump to the value field (alternatively, you can press Right to accept the suggestion and continue editing the field,) or Esc to cancel the change. As usual, Shift-Tab traverses input fields in the reverse order.

• While editing the border-color property value, delete the clue word, and type in bl – in a moment, you will see a suggestion: black.

• Press Up or Down to cycle through all suggestions starting with bl. Choose any color value you like, and press Enter or Tab to accept the suggestion and commit the new property value. The property gets committed, and the exclamation mark disappears, as the property has become valid.

• Besides iterating through available value keywords, you can also increment/decrement numeric property values (like opacity: 0.8 or margin: 2px 4px) with the Up/Downand PageUp/PageDown keys. The unit delta can be controlled in the following ways:
  • 0.1 unit: Alt-Up/Down (or plain Up/Down if the current value is in the range of [-1; 1])
  • 1 unit: Up/Down (for values greater than 1 or less than -1)
  • 10 unit: Shift-Up/Down or PageUp/PageDown
  • 100 unit: Shift-PageUp/PageDown

• Hover the mouse cursor over the rule body. You will see a checkbox to the right of each property in the rule.

• Uncheck a box to disable the border-color property (i.e. temporarily remove it from the style). The property gets struck out, and the change is instantly reflected in the inspected page.

• Double-click the border-color property value and change it to Lime, accept. Notice the property automatically get enabled with the updated value.

Adding New Rules and Properties

• You can add a new style rule to be considered in addition to those found in the stylesheets loaded by the page. Click the Gear  button and select the New Style Ruleoption. A new rule with an automatically suggested selector appears. Press Enter to accept the selector and start typing in the first property of the rule.

  Note: If you edit the selector so that it will not match the selected element, the rule will turn dimmed and obviously, will not be applied to the element. You should rarely need to do this.

• You can also add a new property to any editable style by:
  • Double-clicking the blank space of the first or last rule lines (those with curly braces).
  • Hitting Tab while editing the last style property value (or the corresponding rule selector if no properties have been added yet.)

Metrics Pane

• The Metrics pane resides just below the Styles pane and allows you to examine and edit the current element’s box model parameters found in the computed style.

• The concentric rectangles contain the values for the padding, border, and margin properties (top, right, bottom, and left values for each of them.)

• For non-statically positioned elements, a position rectangle will be additionally displayed in the pane, containing the values of the top, right, bottom, and left properties.

• For position: fixed and position: absolute elements, the central field contains the actual offsetWidth × offsetHeight pixel dimensions of the selected element.

• All values can be modified by double-clicking them, like property values in the Styles pane (the changes are not, however, guaranteed to take effect, as this is subject to the concrete element positioning specifics.)

Persisting Changes

• Upon an external style sheet rule modification, the respective resource text is updated in the Resources panel, and the revision history is stored for such style sheet resources until the DevTools window is closed.

• Activate the Resources panel, find tutorial.css in the resource tree. Note that the tree node is expandable. Click the arrow next to the node title, and you will see all the resource modifications that you have made above.

• Select any revision to see its differences from the original stylesheet resource, highlighted line-wise.

• You can drag and drop a stylesheet revision node into most text editors to export the revision content.