Identify similar value of different tab

Attach a sample workbook. Make sure there is just enough data to make it clear what is needed. Include a BEFORE sheet and an AFTER sheet in the workbook if needed to show the process you're trying to complete or automate. Make sure your desired results are demonstrated, mock them up manually if needed. Remember to desensitize the data.

Click on GO ADVANCED and use the paperclip icon to open the upload window.

View Pic

Conditional Formatting is enough in this case

Place the cursor in A2 cell and extend the selection upto C6 cell. Now your selection will cover A2:C6 range and A2 will be the active cell. Activecell A2 will have a white background after selection also.

Press Alt+O+D>>Click New Rule>>Select Use Formula to determine which cells to format option>>Copy paste the below formula in Format Values where this formula is true box

=COUNTIF('Tab A (Source)'!$A$3:$A$7,A2)

Select format>>select your desired formatting>>Click Ok>>Click Ok>>Click Apply and Ok

Refer the attached file for details