style: vertically align comment bubble icon

The icon of the comment bubble is slightly off-center vertically (too low).
This problem can be solved by reducing the line height instead of using the
default of 20px.

kallithea/public/less/kallithea-diff.less

@@ -1,215 +1,216
 /* bootstrap progress bar has margin-bottom we don't want that in files list */
 .cs_files .progress {
   margin-bottom: 0;
 }
 /* progress bars should be aligned right */
 .cs_files .changes {
   float: right;
   color: @kallithea-theme-main-color;
 }
 
 /* colors for deleted/changed/added, both for 3 labels in top right corner with total count, and for per file "diffstat" (rendered as Bootstrap progress-bar) */
 .changes .added {
   color: inherit;
   background-color: @add-bg-color;
 }
 .changes .changed {
   background: @change-bg-color;
 }
 .changes .deleted {
   background-color: @delete-bg-color;
 }
 /* binary
 NEW_FILENODE = 1
 DEL_FILENODE = 2
 MOD_FILENODE = 3
 RENAMED_FILENODE = 4
 CHMOD_FILENODE = 5
 BIN_FILENODE = 6
 */
 .changes .bin {
   background-color: @add-bg-color;
 }
 /* added binary */
 .changes .bin.bin1 {
   background-color: @add-bg-color;
 }
 /* deleted binary*/
 .changes .bin.bin2 {
   background-color: @delete-bg-color;
 }
 /* mod binary*/
 .changes .bin.bin3 {
   background-color: @change-bg-color;
 }
 /* rename file*/
 .changes .bin.bin4 {
   background-color: #6D99FF;
 }
 /* chmod file*/
 .changes .bin.bin5 {
   background-color: #6D99FF;
 }
 
 /* center collapse button */
 .diff-collapse {
   text-align: center;
   margin-bottom: 15px;
 }
 
 .code-difftable {
   /* the whole line should be colored */
   border-collapse: collapse;
   border-radius: 0px !important;
   width: 100%;
 
   /* line coloring */
   .context {
     background: none repeat scroll 0 0 @highlight-line-color;
     color: #999;
   }
   .add {
     background: none repeat scroll 0 0 #DDFFDD;
   }
   .add ins {
     background: none repeat scroll 0 0 #AAFFAA;
     text-decoration: none;
   }
   .del {
     background: none repeat scroll 0 0 #FFDDDD;
   }
   .del del {
     background: none repeat scroll 0 0 #FFAAAA;
     text-decoration: none;
   }
 
   /* tabs */
   td.code pre u:before {
     content: "\21a6";
     display: inline-block;
     width: 0;
   }
   /* CR */
   td.code pre u.cr:before {
     content: "\21a4";
     display: inline-block;
   }
   /* whitespace characters */
   td.code pre u {
     color: rgba(0, 0, 0, 0.3);
   }
   /* trailing spaces */
   td.code pre i {
     border-style: solid;
     border-width: 0 0 0 1px;
     border-color: rgba(0, 0, 0, 0.3);
   }
 
   /* line numbers */
   .lineno {
     padding-left: 2px;
     padding-right: 2px !important;
     width: 30px;
     border-right: 1px solid @panel-default-border !important;
     vertical-align: middle !important;
     text-align: center;
   }
   .lineno.new {
     text-align: right;
   }
   .lineno.old {
     text-align: right;
   }
   .lineno a {
     color: #aaa !important;
     font-size: 11px;
     font-family: @font-family-monospace;
     line-height: normal;
     padding-left: 6px;
     padding-right: 6px;
     display: block;
   }
   .line:hover .lineno a {
     color: #333 !important;
   }
   /** CODE **/
   .code {
     display: block;
   }
   .code pre {
     border: 0;
     padding: 0;
     margin: 0;
     background: none;
     min-height: 17px;
     line-height: 17px;
     white-space: pre-wrap;
     word-break: break-all;
   }
 
   /* leading +/- on changed lines */
   .del .code pre:before {
     content: "-";
     color: #800;
   }
   .add .code pre:before {
     content: "+";
     color: #080;
   }
   .code pre:before {
     content: " ";
     margin: 0 2px;
   }
 }
 
 /* comment bubble */
 .add-bubble {
   position: relative;
   display: none;
   float: left;
   width: 0px;
   height: 0px;
   left: -8px;
   box-sizing: border-box;
 }
 /* comment bubble, only visible when in a commentable diff */
 .commentable-diff tr.line.add:hover td .add-bubble,
 .commentable-diff tr.line.del:hover td .add-bubble,
 .commentable-diff tr.line.unmod:hover td .add-bubble {
   display: block;
   z-index: 1;
 }
 .add-bubble div {
   background: @kallithea-theme-main-color;
   width: 16px;
   height: 16px;
+  line-height: 14px;
   cursor: pointer;
   padding: 0 2px 2px 0.5px;
   border: 1px solid @kallithea-theme-main-color;
   border-radius: 3px;
   box-sizing: border-box;
   overflow: hidden;
 }
 .add-bubble div:before {
   font-size: 14px;
   color: #ffffff;
   font-family: "kallithea";
   content: '\1f5ea';
 }
 .add-bubble div:hover {
   transform: scale(1.2, 1.2);
 }
 
 /* file diff icons */
 .icon-diff-modified:before {
   color: #d0b44c;
 }
 .icon-diff-removed:before {
   color: #bd2c00;
 }
 .icon-diff-added:before {
   color: #6cc644;
 }
 .icon-diff-renamed:before {
   color: #677a85;
 }