change size, theme and transparency locally

Using global search/replace is dangerous and could lead to unwanted changes. Such practice should be avoided.
This patch surgically makes the change to the very lines where the corresponding values should be updated.

install.sh

@@ -400,7 +400,7 @@ parse_sass() {
 change_size() {
   cd ${SRC_DIR}/sass/gtk
   cp -an _applications.scss _applications.scss.bak
-  sed -i "s/200px/$sidebar_size/g" _applications.scss
+  sed -i "/\$nautilus_sidebar_size/s/200px/${sidebar_size}/" _applications.scss
   prompt -w "Change nautilus sidebar size ..."
 }
 
@@ -409,7 +409,7 @@ change_theme_color() {
 
   cd ${SRC_DIR}/sass
   cp -an _colors.scss _colors.scss.bak
-  sed -i "s/#0860f2/$theme_color/g" _colors.scss
+  sed -i "/\$selected_bg_color/s/#0860f2/${theme_color}/" _colors.scss
 
   cd ${SRC_DIR}/assets/gtk-3.0
   cp -an thumbnail.svg thumbnail.svg.bak
@@ -506,7 +506,7 @@ restore_assets_files() {
 change_transparency() {
   cd ${SRC_DIR}/sass
   cp -an _colors.scss _colors.scss.bak
-  sed -i "s/0.16/$panel_trans/g" _colors.scss
+  sed -i "/\$panel_opacity/s/0.16/${panel_trans}/" _colors.scss
   prompt -w "Change panel transparency ..."
 }