HTML Preview
Use the HTML Preview page to add style sheets which will help SDL Trados Studio preview correctly your HTML documents. You can also specify any other files that might be needed, for example pictures, linked scripts etc.
To open the Preview page for your HTML file type, click File > Options > File Types > [HTML file type] > Preview.
For more information about using style sheets to transform HTML documents, see for example, www.w3schools.com/xsl/xsl_intro.asp
If you do not provide any style sheet transform files, Studio displays the standard tree view of the HTML file.