assuming you know what to change when you know where to change:
the image border:
in default.css:
.posts-default .entry-thumbnails-link { border: 1px solid #E1E1E1; background: #FFF; }
– the white border is created by the background color in combination with this style in base.css:
.posts-default .entry-thumbnails-link { padding: 4px; }
the widget background:
in default.css:
.widgetcontainer { border: solid #CCC; border-width: 1px; background: repeat-x #FFF; line-height: 1.4em; }
the widget-title:
in default.css:
.widgettitle { color: #333; font-size: 12px; font-weight: 700; margin: -10px -10px 10px; padding: 5px 10px; background: url(../../images/feed-title-white.jpg) repeat-x top #EFEFEF; border-bottom: 1px solid #CCC; }
in single posts:
in default.css:
.single .post, #main .single-post { background: #FFF; border: 1px solid #CCC; }
.nocomments { background: #FFF; border: solid #CCC; border-width: 0 1px 1px; padding: 15px 10px; margin: 0 10px 10px 0; font-size: 12px; }
#commentform { background: #FFF; border: solid #CCC; border-width: 0 1px 1px; margin-right: 10px; padding: 10px; }
there will be more …