Suppose we want a link to look like this:
Normal link:

Hover link:

.
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Select Tools -> CSS Style Editor from the main menu. Click the Add button to add a new style. Change the name of the style to "normal-link".
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Select the "Text tab" and set values as shown by the dialog below.
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Select the "Elements tab" and select the options as shown below.
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Click the Add button again to create another style. Change the name to "hover-link.
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Select the "Text tab" and set values as shown below.
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Select the "Elements tab" and select the options as shown below.
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Make sure that "normal-link" comes before "hover-link" in the order as shown below.
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Click OK to save these rules. To use them, just assign these styles to the text elements that have links defined.