1. ADD GADGET
You are currently on the Blogger Layout page, if you see the "sidebar" of Blogger's layout and are showing the option to "Add Gadget" then click on it otherwise scroll down. As it is not visible on our screen, we will scroll down and find "add a gadget" written on the sidebar.
We have got the button "add a gadget". It is not necessary that you find this button on the "sidebar", you can insert your code in other places also. where you see the "add a gadget" button, you can insert your code.
2. CLICK ON HTML/JAVASCRIPT
Click on the html/javascript "+" button and a new window will be popup where you will paste your code.
3. PASTE CODE
Now it's time to paste our code into blogger. First checked the visible button so that your code visible (Readable by the browser) on the blogger. If you want, you can also give the title as we have given in our blog "recent post".
Now paste the code in textarea.
Make sure that your CSS must be inside the "style tag" and the JavaScript must be inside the "script tag".
then click on the save button and your code is inserted in blogger.
6. SAVE LAYOUT
Now save the layout, click on the save icon as you can see in the image. Now you can see your code output.