This Tutorial is in dwi-language. One english, and one malay.
Tutorial ini adalah dalam dwibahasa. Bahasa Melayu ada, begitu juga dengan english.

English :

Here's how:

1) Sign in blogger account

2) Dashboard> Design (or template)> Edit HTML

3) By using ctrl + F (press simultaneously on the keyboard), look for this code

/* Headings

4) Then copy and paste this code AFTER / UNDER / * Headings  code

.post blockquote {background:#FFCCCC;padding: 5px;Border: 2px dashed #FF0099;moz-border-radius: 25px 10px / 10px 25px;border-radius: 25px 10px / 10px 25px;colour:#FF0099;}

You can adjust the values ​​in the above code.
FFCCCC - blockquote background color box. You can refer colour code by clicking >here<
2 - box border line thickness
dashed - line style border. Whether dashed, solid or dotted
FF0099 - border line color. Refer to the color code below
Code purple color - border box design. You can choose your border

5) When you are finished adjust the values ​​above, click preview, and if there is no error, click save template.

/* Headings

 4) Kemudian copy dan paste kod ini SELEPAS / DI BAWAH kod /* Headings tadi

.post blockquote {background:#FFCCCC;padding: 5px;Border: 2px dashed #FF0099;moz-border-radius: 25px 10px / 10px 25px;border-radius: 25px 10px / 10px 25px;colour:#FF0099;}

Nilai yang anda boleh adjust dalam kod di atas
FFCCCC - warna background kotak blockquote. Rujuk kod warna >disini<
2 - ketebalan garisan border kotak
dashed  - style garisan border. Sama ada dashed, solid atau dotted
FF0099 - warna garisan border. Rujuk kod warna di bawahKod warna purple - bentuk kotak border. 

5) Bila dah selesai adjust nila-nilai di atas, klik preview dan jika tiada error, klik save template.

Selamat mencuba! :)